Why do cats meow at humans but not at each other?

Adult cats rarely meow at each other. Meowing is mostly a kitten's sound: a high-pitched 'mew' that kittens use to get their mother's attention, and by four to five months old a kitten stops mewing altogether. So why do house cats meow at us so much? Domestication has significantly changed how cats communicate: domestic cats meow much more than feral cats, and they rarely meow to communicate with other cats or animals. Since adults rarely meow to each other, their meowing at humans is likely a post-domestication extension of the kitten's mew, a baby call now aimed at people.

Once a cat has a human audience, the meow becomes surprisingly flexible. The same sound can be assertive, plaintive, friendly, demanding, or even silent: an open mouth with no noise at all. A cat's vocal tract can't reproduce human words, but cats can shape their meow to mimic words they hear often, so a cat whose owner keeps saying 'no' may learn to say 'mow' in a low tone.

Meowing isn't the only sound with a specific audience. The chirrup, a trill that sounds like a meow rolled on the tongue, is how mother cats call kittens into the nest, and kittens recognize their own mother's chirp while ignoring other mothers' chirps. Cats also chirrup in a friendly way when greeted by another cat or a human, which is why people can mimic the sound to reassure a pet cat. Purring remains the most mysterious: scientists still aren't sure why cats do it, but researchers at the University of Vienna found that a cat's larynx can make the purring sound just from air passing through it, no muscle contraction needed, thanks to connective tissue in the vocal folds that lowers the pitch. Big cats like tigers, lions, jaguars, and leopards can make similar sounds, though only while breathing out.

Cats also 'talk' without a sound. Kneading with the front paws seems to be a leftover kitten habit, thought to come from the motion kittens use to stimulate milk flow while nursing, and many adult cats purr while doing it, usually taken as a sign of contentment. Rubbing their cheeks on objects in their territory deposits a pheromone from glands in the cheeks, known as a contentment pheromone.