Purr

A purr is a tonal fluttering sound made by some species of felids, and two species of genets. It varies in loudness and tone among species; and in the same animal.

Although purring is commonly associated with felids, other animals such as raccoons purr. Other purring animals include viverrids (civet), mongoose, bears, badgers, hyaenas, rabbits, squirrels, guinea pigs, tapirs, ring-tailed lemurs, and gorillas while eating.

The mechanism by which cats purr is speculative. There is a unique "neural oscillator" in the cat’s brain of uncertain significance.

One hypothesis, backed by electromyographic studies, is that cats produce the purring noise by using the vocal folds and/or the muscles of the larynx to alternately dilate and constrict the glottis rapidly, causing air vibrations during inhalation and exhalation. Combined with the steady inhalation and exhalation of air as the cat breathes, a purring noise is produced with strong harmonics. Despite competition from various contenders, the record for the loudest purring cat continues to be held by Smokey, owned by Ruth Adams (UK). On 25 March 2011, Smokey purred at 67.7 dB.

No cat can both purr and roar. The subdivision of the Felidae into "purring cats" on the one hand and "roaring cats" on the other, originally goes back to Owen (1834/1835) and was definitively introduced by Pocock (1916), based on whether the hyoid bone of the larynx is incompletely ("roarers") or completely ("purrers") ossified. However, Weissengruber et al. (2002) argued that the ability of a cat species to purr is not affected by the anatomy of its hyoid.

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