Why do cats purr? The short answer is: we don’t know for sure.
What we do know about purring:
A feline purr is produced using the diaphragm and the laryngeal muscles (at the opening to the windpipe where the vocal cords live). The muscles twitch between 25 and 150 times per second, causing the vocal folds to separate. It continues during both inhaling and exhaling. It is theorized that this frequency improves bone density and promotes healing of bones and muscles. It can also have pain-relieving properties. So purring may be a mechanism for self-healing, and might explain why we see fewer bone problems with cats than with dogs. Members of the felidae family (bobcat, cheetah, lynx, and puma) all purr, but the pantherinae family (lion, tiger, jaguar, leopards) have a different vocalization.
When do cats purr?
Cats purr in a variety of situations and in response to different stimuli. Things that can stimulate feline purring include:
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