According to the author of The Cat Behavior Answer Book, Arden Moore, cats are capable of up to 30 sounds. Few are more recognizable than the cat’s purr. Cats are the most mysterious of pets, carrying an air of mystery about them, but there are some things we’ve managed to decipher in cat-human relations.
So what is your cat trying to tell you when they purr? It’s actually a very complicated question. Purring is a natural behavior, but also a learned one. Cats are born deaf and blind, so they use vibration early on in life.
A cat’s purring begins in their brain, a rhythmic, repeating neural oscillator sends messages to the muscles in their larynx. This causes cats to twitch at 25 to 150 vibrations per second, creating the vibrato you hear. But what does it mean?
“I’m Content”

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This is probably the most obvious, as you usually hear it when your cat is really into your petting. If they’re curled in your lap and particularly comfortable, they might express their enjoyment through purring. It’s another way of smiling for them.