Purr

A purr or whirr is a tonal fluttering sound made by some species of felids, including both larger, wild cats and the domestic cat (Felis catus), as well as two species of genets and the Caquetá titi monkey (Plecturocebus caquetensis). It varies in loudness and tone among species and in the same animal. Although true purring is exclusive to felids and viverrids, other animals such as raccoons produce vocalizations that sound similar to true purring. Animals that produce purr-like sounds include mongooses, kangaroos, wallabies, wallaroos, badgers, otters, rabbits, foxes, lemurs, and guinea pigs.

Animals purr for a variety of reasons, chiefly to express happiness, but also as defense mechanism for pain. Cats also purr to manage pain and soothe themselves. Purring is a soft buzzing sound, similar to a rolled 'r' in human speech, with a fundamental frequency of around 25 Hz. The sound occurs with noticeable vibrations on the surface of the body, varies in a rhythmic pattern during breathing and, for cats, occurs continuously during inhalation and exhalation, while other animals (such as foxes) only purr on exhale. The intensity and length of the purr can also vary depending on the level of arousal of the animal.