Along with sleep, grooming is probably one of the cat's biggest activities, to such an extent that Pasteur is credited with saying, "cats are clean animals because they spend all day grooming themselves."
In addition to the cleaning function in the strict sense of the word, grooming has an important calming effect. When cats lick themselves or when they are licked by another (as with kittens licked by their mother), endorphin production is triggered, the same hormones that are produced to counteract the sensation of pain. An anxious cat, for example, will lick itself more frequently than another cat, even at the risk of mutilating itself and pulling out hair. Because it can be done to others, the licking behavior has a social function that is clearly illustrated in the mother-kitten relationship.
Functional as of the 15th day of life, grooming is done with the particularly rough tongue and also with the paws. The front paw is moistened with the tongue and then serves as a sort of washcloth to reach the ears. The back paws are used to reach the ears and the back, sometimes with a little too much zeal. We can see the classic autopodal reflex Ð the paws begin to move when the side of a parasite-infected ear, typically mange, is scratched. However, we may also see another, non-pathological reflex when we stroke the cat's lower back Ð the cat's tongue makes licking movements in time with the stroking!