purring

Purring is a vocal phenomenon most closely associated with domestic cats, though it occurs in several other small felids. It refers to a low, continuous vibrating sound produced by rhythmic movement of the vocal folds and surrounding laryngeal muscles, usually during inhalation and exhalation. While cats commonly purr when content, they may also purr during stress, illness, or nursing, indicating that the behavior is not solely tied to a positive emotional state.

Mechanistically, purring arises from the brain sending repetitive motor signals to the laryngeal muscles, causing the glottis to open and close rapidly. This rapid airway modulation creates the characteristic vibration of the vocal cords and a steady, rolling sound as air moves in and out. The audible frequency of cat purrs generally falls in the range of about 25 to 150 Hz, with variations in amplitude and harmonic structure depending on the individual and context.

Species and variation: Domestic cats are the best-known purring subjects, and many related small felids can purr as well. The ability to produce a true, continuous purr is common in several modern felids, though some larger cats and those with different throat anatomies may produce purring-like sounds or roars rather than the classic purr.

Functions: Purring is thought to play multiple roles, including communication with humans and other animals, self-soothing, and possibly promoting healing or tissue regeneration, though evidence for medical benefits remains inconclusive. The behavior is studied primarily in domestic cats and has a strong association with comfort and bonding.