He did it. It was as though this dog had learned the concept imitate, imitate, and, given that notion, could apply it more or less in any direction. To do this, he had to map his body onto a human's: where a person tossed a bottle by hand, the dog used his mouth; he used his nose to push the swing. This is not the final word about imitation (just ask your dog to copy your swing-pushing, and you can see how results do not always generalize), but these dogs' abilities are suggestive of something besides mindless mimicry. Dogs may be enabled to imitate by the same ability-almost compulsion-to look at us that allows them to use us to learn how to act. That is what I see in Pump's morning stretch alongside me. and, given that notion, could apply it more or less in any direction. To do this, he had to map his body onto a human's: where a person tossed a bottle by hand, the dog used his mouth; he used his nose to push the swing. This is not the final word about imitation (just ask your dog to copy your swing-pushing, and you can see how results do not always generalize), but these dogs' abilities are suggestive of something besides mindless mimicry. Dogs may be enabled to imitate by the same ability-almost compulsion-to look at us that allows them to use us to learn how to act. That is what I see in Pump's morning stretch alongside me.

THEORY OF MIND.

I open the door stealthily and Pump's there, not two feet away, walking toward the rug with something in her mouth. She stops in her tracks and looks over her shoulder at me, her ears down, her eyes wide. In her mouth is an unidentifiable curved form. As I slowly approach, she wags low, ducks her head, and in the moment that she opens her mouth to get a better grip on her find I see it: the cheese left out on the counter to warm. The brie. The entire enormous round of brie. She gulps two gulps and it's gone, down the gullet.

Think of the dog caught in the act of stealing food from the table ... or looking at you squarely in the eyes with a plea to go out, be fed, be tickled. When I see Pump, mouth full of brie, seeing me, I know she's going to make a move; when she sees me seeing her, does she know I'm going to try to thwart it? My strong impression is that she does: the moment I open the door and she looks at me, we both know what the other is going to do.

The study of animal cognition reaches its pinnacle in addressing just this kind of scene: one raising the question of whether an animal conceives of others as independent creatures with their own, separate minds. This ability seems more than any other skill, habit, or behavior to capture what it is like to be a human: we think about what others are thinking. This is called having a theory of mind. theory of mind.

Even if you've never heard of theory of mind, chances are you nonetheless have a very advanced one. It allows you to realize that others have perspectives different from your own, and therefore have their own beliefs; different things they know and don't know; a distinct understanding of the world. Without one, others' behavior, even the simplest acts, would be utterly mysterious, arising from unknown motivations and leading to unpredictable consequences. Trying to guess what a man approaching you, mouth agape, arm raised high, hand waving frantically, is going to do is greatly aided by having a theory of mind. It's called a theory theory because minds are not directly observable, so we extrapolate backward from actions or utterances to the mind that prompted that act or remark. because minds are not directly observable, so we extrapolate backward from actions or utterances to the mind that prompted that act or remark.

We aren't born thinking about others' minds, of course. It is quite likely that we aren't born thinking about much at all, even our own minds. But each normal child develops a theory of mind eventually, and it appears that it is developed through the very processes discussed so far: through attending to others, and then noticing their attention. Children with autism often don't develop some or any of these precursory skills: they may not make eye contact, point, or engage in joint attention-and many don't seem to have a theory of mind. For most people, it is but one large theoretical step from an awareness of the role of gaze and attention to realizing that there is a mind there.

The gold standard experiment for theory of mind is called the false belief false belief test. In this design, the subject, typically a child, is presented with a minidrama played out by puppets. One puppet places a marble in a basket in front of her, in full view of the subject and a second puppet. Then the first puppet leaves the room. Promptly, the second puppet wickedly moves the marble over to her basket. As the first puppet returns, the subject is quizzed: Where will the first puppet go looking for her marble? test. In this design, the subject, typically a child, is presented with a minidrama played out by puppets. One puppet places a marble in a basket in front of her, in full view of the subject and a second puppet. Then the first puppet leaves the room. Promptly, the second puppet wickedly moves the marble over to her basket. As the first puppet returns, the subject is quizzed: Where will the first puppet go looking for her marble?

By age four, children answer correctly, realizing that they and the puppet know different things. Before that age, though, children surprisingly and unambiguously fail. They say the puppet will look for the marble where the marble actually is-in the second basket-showing that they aren't thinking about what the first puppet really knows.

To design a verbal false belief task for animals, who cannot be expected to communicate their answers (nor be engaged by a puppet marble-switching drama) is nigh impossible, so nonverbal tests have been developed. Many take their cue from anecdotal reports of compellingly mindful animal behavior seen in the wild: of deception or clever compet.i.tive strategies. Chimpanzees are the most frequent subjects since, as close relatives to humans, one might expect that they would have the most similar cognitive abilities.

While the results with chimpanzees have been equivocal, lending credibility to the notion that only humans have a fully developed theory of mind, a wrench has been thrown in the experimental works. That wrench is the dog: whose attention to attention, whose seeming mind reading, looks anecdotally just like what we call acting with a theory of mind. To go from my living-room theorizing about a dog's understanding of mind to solid scientific standing, researchers have begun to run dogs on the same tests used with chimps.

THEORY OF DOG MIND.

Here's what one dog, an unsuspecting experimental subject, found awaiting him at home one day. Instead of the usual ready availability of his favorite tennis b.a.l.l.s, every ball in the house had been collected, and an extra lot of people were standing about gazing at him. Fine so far: Philip, the three-year-old Belgian Tervuren in question, didn't freak out. But he might have been bemused when, one by one, the b.a.l.l.s were shown to him and then placed in one of three boxes and locked up. This was new stuff. Whether game or threat, what was clear was that the b.a.l.l.s were being methodically placed somewhere other than his favorite place: right in his mouth.

When released by his owner, Philip went, naturally, straight toward the box where he saw a ball hidden, and he nuzzled the box. This turned out to be the right thing to do, for it prompted the humans to exclaim merrily, open the box, and give him the ball. Despite just having his mouth on the ball, the dog found that the people around him kept taking it away and securing it in one or the other box-so he kept playing along. Then they started locking the boxes and putting the key elsewhere, so the whole thing took even longer after he selected the right box: someone must find the key, bring it to the box, and open it. The final twist involved one person who locked the box, hid the key, then left the room. Another person came in-surely one who, like all other people around, would be able to use these key-things to open these lock-things.

This was the moment the experimenters were waiting for: they wanted to know if the dog saw the new person as unknowledgeable about the location of the key. If so, then not only should Philip indicate which box has the beloved ball, he should also help the person find the key that would enable access to that ball.

On repeated trials, that's more or less what the dog did: ever patient, Philip looked toward the spot where the key had been hidden, or headed that way. Note that he didn't actually take it in his mouth and open the box: that'd be some trick, but even the most ardent dog enthusiast will admit it's unlikely. Instead, Philip used his eyes and his body as communications.

Philip's behavior could be interpreted in three ways: one functional, one intentional, one conservative. The functional interpretation is this: the dog's gaze served as information for the person, whether the dog meant it to or not. The intentional: the dog did in fact mean it to: he looked because he knew the person was ignorant of the key's location. The conservative: the dog looked reflexively, since someone was recently over there where the key was.

The data do the interpreting. They show that the functional is definitely true: gaze did serve as information to the person nearby. But the intentional take is also true: the dog looked at the location of the key more often when the person in the room with them was ignorant where it was-as if meaning to inform the person with his gaze. That nixes the conservative interpretation. Philip seemed to be thinking about these crazy experimenters' minds.

This is but one dog-maybe a particularly astute one. Remember the begging experiment run with chimps and dogs? Unlike chimps, all the tested dogs immediately followed the knower's (non-blindfolded or bucketed person's) advice as to which box was baited with food. Hoorah for these dogs, who thus all found food inside. This looks good for the theory of dog mind: they acted as though thinking about the knowledge states of the strange people pointing in front of them. But after this seeming cognitive accomplishment, a strange thing happened. When run again and again on the same test, these dogs changed their strategies. They began to pick the guesser just about as often as the knower. Does this mean they were prescient and then grew dimwitted? Although dogs will do impressive convolutions for food, this doesn't make sense as an explanation. Perhaps it indicates that the first round was a fluke.

The best interpretation is that the dogs' performance on the task makes a methodological point. There may be other cues the dogs are using to make their decisions that are, to them, just as strong as the presence or absence of the guesser is to us. Consider, for instance, that all humans are on the whole highly knowledgeable about the sources of food, from a dog's point of view. We are regularly around food, we smell like food, we open and close a cold box filled with food all day long, and sometimes we even have food dribbling out of our pockets. This is such a well-learned feature of us that it might be hard to overturn on the basis of a few trials one afternoon. This hypothesis is borne out by the fact that the dogs did use the people people to make their decision: they never chose a third box, unselected by either the guesser or the knower. to make their decision: they never chose a third box, unselected by either the guesser or the knower.

However we interpret the results, though, the dogs are not going out of their way to prove to us that they have a theory of mind. Of course, one of the difficulties of designing experiments for any animal is that, as the procedure grows more complicated in order to test for a very specific skill, it risks becoming an exceedingly strange scenario for the animal. One might suggest that ma.s.sive confusion on the part of the subjects is not unreasonable. They are often thrust into situations that are bizarre: that are, in fact, intentionally unlike anything they've seen before. People appear with buckets over their heads; trials go on endlessly; it is in every way not normal. Dogs nonetheless sometimes manage to perform well at the tasks in front of them.

Still, their natural behavior-in a natural setting-is a better indication. What do dogs do without the peculiarities of baited and locked boxes and uncooperative humans to puzzle over? Their most representative behavior will appear in dealing naturally with other dogs or with humans. If it is socially helpful for a dog to consider what other dogs are thinking, the ability to do so may have evolved-and may still be visible in social interactions. This is why I spent a year watching dogs play: playing in living rooms and veterinary offices, down hallways and pathways, on beaches and in parks.

PLAYING INTO MIND.

Pump appears in the corners of all the videos: in one, she hops nimbly to avoid collision with a dog approaching too fast-then pursues him as he rushes out of the frame. In another, she lies p.r.o.ne with another dog, feigning bites with open mouths. In a third she tries and fails to join two dogs in play; as they run off she is left wagging alone in the camera's eye.

I should correct myself: I was lucky enough lucky enough to spend a year watching dogs play. What is called, appropriately, "rough-and-tumble" play between two competent, athletic dogs is a gymnastic marvel to witness. The playing dogs seem to give a perfunctory greeting to each other before they suddenly mutually attack, teeth bared; tumbling together in precarious free fall; jumping on and over each other; bodies bent and tangled. When they stop, suddenly, at a noise nearby, they may be the pictures of quiet. It takes only a look or a paw raised in the air to engage in their shared havoc again. to spend a year watching dogs play. What is called, appropriately, "rough-and-tumble" play between two competent, athletic dogs is a gymnastic marvel to witness. The playing dogs seem to give a perfunctory greeting to each other before they suddenly mutually attack, teeth bared; tumbling together in precarious free fall; jumping on and over each other; bodies bent and tangled. When they stop, suddenly, at a noise nearby, they may be the pictures of quiet. It takes only a look or a paw raised in the air to engage in their shared havoc again.

Play might seem just like that thing dogs do, that thing dogs do, but it has a very particular scientific definition. Animal play, science intones, is a voluntary activity incorporating exaggerated, repeated behaviors, extended or truncated in duration, varied in fort.i.tude, and atypically combined; and using action patterns that have identifiable, more functional, roles in other contexts. We don't just define play this way to take the pleasure out of it: we define it to reliably recognize it. Play also has all the attributes of a good social interaction: coordination, turn taking, and, if necessary, self-handicapping-playing at the level of one's play partner. Each partner takes the abilities and behavior of the other into account. but it has a very particular scientific definition. Animal play, science intones, is a voluntary activity incorporating exaggerated, repeated behaviors, extended or truncated in duration, varied in fort.i.tude, and atypically combined; and using action patterns that have identifiable, more functional, roles in other contexts. We don't just define play this way to take the pleasure out of it: we define it to reliably recognize it. Play also has all the attributes of a good social interaction: coordination, turn taking, and, if necessary, self-handicapping-playing at the level of one's play partner. Each partner takes the abilities and behavior of the other into account.

The function of animal play is a bit of a puzzle. Most animal behaviors are described by how they function to improve the survival of the individual or species. The search for a function of play is paradoxical, as it looks like behavior which is clearly function less: less: at the end of play, no food has been gained, no territory secured, no mate wooed. Instead two dogs pantingly collapse on the ground and wag their tongues at each other. One might thus suggest that the function is at the end of play, no food has been gained, no territory secured, no mate wooed. Instead two dogs pantingly collapse on the ground and wag their tongues at each other. One might thus suggest that the function is to have to have fun fun-but this is frowned upon as a true function, because the risks are too great. Play takes a lot of energy, can cause injuries, and, in the wild, increases an animal's danger of predation. Play-fighting can escalate into true fights, causing not just injury but social upheaval. Its riskiness makes the case for a real, undiscovered function of play even more compelling: it must be terribly useful to play, if this behavior survived the evolutionary process. It might serve as practice: a context in which to hone physical and social skills. Strangely, though, studies have shown that play is not essential to adult proficiency at the skills practiced in play. Maybe play serves as training for unexpected events. It does seem that volatile and unpredictable play is deliberately sought. In humans, play is part of normal development-socially, physically, and cognitively. In dogs, it may be the result of having spare energy and time-and owners who live vicariously through their dogs' tumblings.

Play among dogs is particularly interesting because they play more than other canids, including wolves. And they play into adulthood, which is rare for most playing animals, including humans. Although we ritualize play into team sports and solo video game marathons, as sober adults we rarely spontaneously blindside and tackle our friends, tag them and run, or make faces at each other. The hobbling, slow-moving fifteen-year-old dog on the block looks warily at the enthusiasm of young puppies approaching him, but even he occasionally play-slaps and bites at a younger dog's legs in play.

In my study of dog play I shadowed dogs around with a video camera rolling, and controlled my own delighted laughter at their fun long enough to record bouts of play, from a few seconds to many minutes long. After a few hours of this the fun stopped, the dogs would get packed into the backs of cars, and I would walk home, reflecting on the day. I'd sit down in front of my computer and play back the videos, at an extremely slow rate: slowed enough to see each frame-thirty of which fill a second-individually. Only at this speed could I really see what had happened in front of me. What I saw was not a repeat of the scene I'd witnessed at the park. At this speed I could see the mutual nods that preceded a chase. I saw the head-jockeying, open-mouth volleys that blurred into unrecognizability in real time. I could count how many bites it takes, over the course of two seconds, before a bitten dog responds; I could count how many seconds it takes for a paused bout to resume.

And, most important, I could look to see what behaviors dogs do, and when. Watching the play deconstructed into these subsecond moments enabled me to record a long catalog of the behaviors of each dog: a transcript of the play. I also noted their postures, their proximity to one another, and which way they were looking at every moment. Then, so deconstructed, the play could be reconstructed to see what behaviors match what postures.

In particular, I was interested in two kinds of behaviors: play signals and attention-getters. Attention-getters, as we've seen, are obvious things: they serve to get attention. Specifically, they are acts that alter the sensory experience of someone else-someone whose attention you're keen to have on you. They can be an interruption of the visual field, as when Pump suddenly puts her head between me and the book I'm holding. They can interrupt the auditory environment: a car's honk is so intended, and dogs' barks are so as well. If these methods fail, attention can be gotten by interacting physically: a hand on the shoulder; a paw on the lap; or, between dogs, a b.u.mp with the hip or a light bite on the rump. Clearly, many things we do are in some way attention-getting, but not every behavior is equally good at the task.

Calling your name out may be a way to catch your attention-but not if we are in Yankee Stadium in the bottom of the ninth. Then a more extreme method (and possibly an organist) would be necessary. Similarly, dogs' attention can be more or less easy to get. Between dogs, what I called an in-your-face in-your-face-presenting oneself in front of, and very close to the face of, another dog-is effective at getting attention-but not if the dog is engaged in rollicking play with someone else. Then more forceful means are needed-thus explaining those dogs who circle a playing pair for minutes barking barking barking. (Better, perhaps, to interject some nice rump bites in there with the barking, if you are truly eager to break up the game.) Play signals, the other behaviors, are requests for play or announcements of interest in playing: they could be translated as saying something like Let's play Let's play or or I I want to play want to play or even or even Ready? because I'm about to play with you. Ready? because I'm about to play with you. What the specific words are is not as important as their functional effect: play signals are reliably used to begin and to continue play with others. They are a social requirement, not just a social nicety. Dogs typically play together rambunctiously and at a breakneck pace. Since they are doing all manner of actions that could easily be misinterpreted-biting each other on the face, mounting from behind or fore, tackling the legs out from under another dog-the playfulness of their actions has to be manifest.* If you fail to signal before biting, jumping on, hip-slamming, and standing over your playmate, you are not in fact playing; you are a.s.saulting him. A bout wherein only one partic.i.p.ant thinks it's play is no longer playful. All dog owners who walk their dogs among others know what then happens: a play bout becomes an attack. Without the play signal, a bite is a bite, worthy of rancor or retribution. With it, a bite is just part of the game. What the specific words are is not as important as their functional effect: play signals are reliably used to begin and to continue play with others. They are a social requirement, not just a social nicety. Dogs typically play together rambunctiously and at a breakneck pace. Since they are doing all manner of actions that could easily be misinterpreted-biting each other on the face, mounting from behind or fore, tackling the legs out from under another dog-the playfulness of their actions has to be manifest.* If you fail to signal before biting, jumping on, hip-slamming, and standing over your playmate, you are not in fact playing; you are a.s.saulting him. A bout wherein only one partic.i.p.ant thinks it's play is no longer playful. All dog owners who walk their dogs among others know what then happens: a play bout becomes an attack. Without the play signal, a bite is a bite, worthy of rancor or retribution. With it, a bite is just part of the game.

Nearly every play bout begins with one of these signals. The quintessential signal is the play bow, play bow, in which the dog's body genuflects in front of a desired play partner. A dog bent on his forelegs, mouth open and relaxed, with his rump in the air and tail high and wagging is pulling out all the stops to induce someone to play. Even tailless, you can mimic this pose yourself; expect a response in kind, a friendly nip, or at least a second look. Two dogs who are regular playmates may use a bow shorthand: familiarity allows abbreviations in formality, just as between human acquaintances. Just as in which the dog's body genuflects in front of a desired play partner. A dog bent on his forelegs, mouth open and relaxed, with his rump in the air and tail high and wagging is pulling out all the stops to induce someone to play. Even tailless, you can mimic this pose yourself; expect a response in kind, a friendly nip, or at least a second look. Two dogs who are regular playmates may use a bow shorthand: familiarity allows abbreviations in formality, just as between human acquaintances. Just as How do you do? How do you do? became became Howdy, Howdy, the play bow can be shortened into the aforementioned the play bow can be shortened into the aforementioned play slap, play slap, the front legs clapping the ground at the beginning of the bow; the the front legs clapping the ground at the beginning of the bow; the open mouth display, open mouth display, the mouth opened but without the teeth bared; or the the mouth opened but without the teeth bared; or the head bow, head bow, a bobbing of the head with opened mouth. Even panting in quick bursts can be a signal to play. a bobbing of the head with opened mouth. Even panting in quick bursts can be a signal to play.

It is how dogs might use these play-signal and attention-getting behaviors together that could reveal or refute that dogs have a theory of mind. In just the way the false belief task shows that some children are thinking about what other people know, and some are not, one's use of attention in communicating is meaningful. The key question I asked of my data of playing dogs was this: Did they communicate, using play signals, intentionally-with attention to the attention of their audience? And did they use attention-getters when they didn't have their play partner's attention? Just how were those b.u.mps, barks, and bows of play used?

It's hard to give a good account of what's happened in a bout of play you have just watched. Sure, I could create a very simplistic story line between two dog protagonists-Bailey and Darcy ran around together ... Darcy chased Bailey and barked ... they both bit at each other's faces ... then they split barked ... they both bit at each other's faces ... then they split-but it glosses over the details, such as how often Darcy and Bailey self-handicapped, intentionally throwing themselves on the ground on their backs to be bitten, or using less force in a bite than they could. Whether they took turns in biting and being-bitten; chasing and being-chased. And, most critically, whether they signaled to each other when the signal could be seen and responded to-with play or by hightailing it out of there. For this, you need to look at the moments between the seconds.

What I found there was remarkable. These dogs play-signaled only at very particular times. They signaled reliably at the beginning of play-and always to a dog who was looking at them. Attention might be lost a dozen times in a typical play session. One dog gets distracted by a ripe smell underfoot; a third dog approaches the playing pair; an owner wanders away. What you might notice is simply a pause followed by a resumption of play. In fact, in these cases, a quick series of steps needs to be followed. For the play not to be permanently severed, the interested dog must regain his partner's attention and then ask him to play again. The dogs I observed also play-signaled when the play had paused and they wanted to resume the game-again, almost exclusively to dogs able to see the signal. In other words, they communicated intentionally, to an audience able to see them.

Even better, in many cases the record of where the dogs were looking revealed that a dog who had paused play was distracted-looking elsewhere, playing with someone else. One option for his erstwhile partner would be to play-bow madly, hoping to lure someone over to play. But more mindful would be just what they did: used an attention-getter before doing a bow. Importantly, they used attention-getters that matched matched the level of inattention of their playmates, showing they understood something about "attention." Even in the middle of play, they used mild attention-getters-such as an the level of inattention of their playmates, showing they understood something about "attention." Even in the middle of play, they used mild attention-getters-such as an in-your-face in-your-face or an or an exaggerated retreat, exaggerated retreat, leaping backward while looking at the other dog-when their partner's attention was only mildly diverted. If a dog's desired playmate was just standing there staring at him, these attention-getters might indeed be enough to rouse him, as a wave leaping backward while looking at the other dog-when their partner's attention was only mildly diverted. If a dog's desired playmate was just standing there staring at him, these attention-getters might indeed be enough to rouse him, as a wave h.e.l.lo? h.e.l.lo? in front of a daydreaming friend. But when the other dog was very distracted, looking away or even playing with another dog, they used a.s.sertive attention-getters-bites, b.u.mps, and barks. In these cases, that mild in front of a daydreaming friend. But when the other dog was very distracted, looking away or even playing with another dog, they used a.s.sertive attention-getters-bites, b.u.mps, and barks. In these cases, that mild h.e.l.lo? h.e.l.lo? would not do. Instead of using a brute-force method of trying to get attention by any means necessary, they chose types of attention-getters that were just sufficient, but not superfluous, to get the desired attention. This was truly sensitive behavior on the part of the players. would not do. Instead of using a brute-force method of trying to get attention by any means necessary, they chose types of attention-getters that were just sufficient, but not superfluous, to get the desired attention. This was truly sensitive behavior on the part of the players.

Only after these attention-getters were successful did the dogs signal their interest in playing. In other words, they were using an order of operations: get attention first, then send an invitation to rumble.

This is just what good theorists-of-mind do: think about their audience's state of attention and only talk to those who can hear and understand them. The dogs' behavior looks tantalizingly close to a display of theory of mind. But there's reason to believe that their ability is different than ours. For one thing, in both the experiments and my play study, not all dogs acted equally mindfully. Some dogs are oblivious in their attention-getting. They bark, get no response-and then bark and bark and bark and bark. Others use attention-getters when attention has already been gotten, or play signals when play has already been signaled. The statistics show that most dogs act mindfully, but there are plenty of exceptions. We can't tell yet whether they are just the underperformers or whether they indicate that the species has an incomplete understanding.

It may be a little of both. Rather than contemplating the mind behind the dog, most dogs are likely to simply interact. Their skill at using attention and play signals hints that they may have a rudimentary rudimentary theory of mind: knowing that there is some mediating element between other dogs and their actions. A rudimentary theory of mind is like having pa.s.sable social skills. It helps you play better with others to think about their perspective. And however simple this skill may be, it may be part of an inchoate system of fairness among dogs. Perspective-taking underlies our agreement to a code of conduct between humans that is jointly beneficial. Watching play, I noticed that dogs who violated the implicit rules for attention-getting and play-signaling-simply barging in on others' play without following the proper, mindful procedures, say-were shunned as playmates.* theory of mind: knowing that there is some mediating element between other dogs and their actions. A rudimentary theory of mind is like having pa.s.sable social skills. It helps you play better with others to think about their perspective. And however simple this skill may be, it may be part of an inchoate system of fairness among dogs. Perspective-taking underlies our agreement to a code of conduct between humans that is jointly beneficial. Watching play, I noticed that dogs who violated the implicit rules for attention-getting and play-signaling-simply barging in on others' play without following the proper, mindful procedures, say-were shunned as playmates.*

Does this mean that your dog is aware of and interested in what's on your mind right now? No. Does it mean that he might realize that your behavior reflects what's on your mind? Yes. Used to communicate with us, this is a large part of dogs' seeming humanity. Sometimes it is even used in nefarious ways only too human.

WHAT HAPPENED TO THE CHIHUAHUA.

We can now revisit the wolfhound and Chihuahua we met at the start of this book. Their hillside encounter is no less remarkable now, but it does perfectly encapsulate the flexibility and variety of behaviors of the species. The explanation for that play begins in the history of their social ancestors, the wolves; it is apparent in the hours of socializing between humans and dogs; in the years of domestication; in the dialogues of speech and behavior between us. It is explicable in the sensorium of the dog: the information he gets from his nose, what his eyes take in. It is in the capacity of dogs to reflect on themselves; it is explained in their different, parallel universe.

And it is in the particular signals they use with each other. The wolfhound's high-rumped approach: the play bow, an invitation to a game-making perfectly clear his ardent intent to play with, not eat, the little dog. In return, the Chihuahua bowed: accepting the offer. In the language of dogs that is enough to see each other as equals in play. Their disparate sizes aren't irrelevant-and this explains the hound's drop to the ground: he handicaps himself. By putting himself at the little dog's height-taking the Chihuahua's point of view-and exposing himself to her attacks, he levels the playing field.

They endure jostling body on body. Bodies in full contact is a reasonable social distance for dogs. They bite with impunity: every bite is matched, or explained with a play signal-and every bite is restrained. When the hound hits the little dog too hard, sending her scurrying backward, she could for a moment be seen as small, fleeing prey. But the difference between dogs and wolves is that dogs can put aside their predatory instincts. Instead the hound takes back that swipe with an apologetic play slap, a milder version of the bow. It works: she rushes right back into his face.

Finally, when the hound is pulled up and away by his owner, the Chihuahua tosses a bark to her departing playmate. Had we kept watching them, had he turned around, we might have seen her open her mouth or leap a tiny leap-calling out in the hopes of continuing the game with her giant friend.