Answer: It is believed that the original purpose of purring was to serve as a signal from the suckling kitten to its mother that it was contented, and kittens from about one week of age are able to purr. Its special value is that because this sound can be produce with the mouth closed the kitten does not have to let go of the teat.
As the cat gets older, purring is used in other situations, again usually to signify of sense of well being. For example, mother cats purr both when approaching their kittens and during suckling to re-assure the young that all is well.
And of course cats use purring as a greeting and sign of the affection for their owner. Purring as a greeting between cats is sometimes show by a young cat wanting to play with a older or by a dominant but friendly cat which wishes to reassure an inferior or younger cat that it means no harm. By purring whilst rubbing against the owner’s leg, or when being stroked on the owner’s lap, the cat is behaving rather as a kitten does towards its mother. Indeed, some cats even show a ‘kneading’ action when being held (a gentle up and down moment of the forelegs) which resembles the way in which kittens ‘kneads’ the mammary gland of the mother during suckling. A few cats even show this obviously pleasurable reaction on a fur rug or pile of washing kneading and purring with great satisfaction.
Paradoxically, an injured, ill or timid cat may sometimes purr when it feels threatened in some way, for example by more dominant animal. In this context, a deep purring appears to act not as a sign of well being but rather as a plea for mercy.
Cats appear to purr less frequently as they get older, although with age they can use tow or three notes in purring compared with the single note of kittens.
