Whilst quite a few humans are allergic to cats, they can also be allergic to us humans. Cats can also suffer from asthma.

Domestic cats aren't as domestic as we claim. They still share most of their DNA with their wild variants and have kept their wild instincts. In comparison, dog have grown out of most of their wolf like behavior.

Cat brains are 90% similar to human brains. Thus if your instinct tells you, that your cat is planning something, your cat is most definitely planning something. Beware the felines.

Cats only meow at humans. It is as if they have developed a way to control humans and it seems to work extremely well. Over time, cat owners instinctively know what their cat wants based on its meows. Slowly but surely, cats have started to hypnotize humans to bring them food and clean their toilets.

Cat purrs vibrate at a frequency that can improve bone density and promote healing. Thus it is actually quite common to spot cats purring at injured cats. This isn't just a sign of affection/sympathy but also an attempt to help a fallen comrade.