One of the most well-known characteristics of a domestic cat is the sound of her purr. It is a pleasing sound when your furry, purring feline curls up next to you. Despite how common and distinct this sound, we do not have full understanding about why and how cats purr.
The most common school of thought about the purpose of purring is that the cat is happy, content, relaxed or expressing pleasure. Dr. Barbara Sherman from the North Carolina State Veterinary Health Complex speculates that purring is a means of communicating positive interactions toward other cats, including offspring, and to humans. They purr in a variety of situations, such as before nursing kittens, sleeping, greeting other cats, and of course, interacting with their owner or caregiver.
The reason behind purring is still in debate because there are other situations in which cats have been found purring. Leslie A. Lyons from the University of California- Davis says that cats have been known to purr when under stressful or frightening situations, such as a trip to the vet, or even when in pain. One reason a cat may purr during these situations, according to the Houston Vet Clinic, is to communicate to other cats that she is not a threat.
Dr. Elizabeth Von Muggenthaler published an article in the "Journal of the Acoustical Society of America" suggesting that, based on research, purring is a mechanism of healing from injury. The purr vibrates at a sound frequency between 20 and 150 Hertz. This low frequency has been shown to be therapeutic and to promote the growth, strengthening and healing of bone and muscle, and to be part of wound healing, tendon repair, pain relief, inflammation reduction and dyspnea relief.
How a cat purrs is still not entirely clear; a cat has no unique anatomical features to cause the purr. A cat can purr while both inhaling and exhaling and also while making other sounds, such as crying. The common theory agreed upon is that the purring sound is caused by rapid muscle contractions of the vocal folds in the larynx. Combined with the air pressure during breathing, the rapid contractions cause sound bursts, or vibrations, every 30 to 40 milliseconds, which cause the purring sound.
Who Can Purr
In addition to the common domestic cat, other species in the Felidae family can purr, such as the puma, cheetah, ocelot, bobcat, lynx and wildcat. The big cats in the subfamily Pantherinae, such as the lion, panther, tiger, jaguar and leopard, do not truly purr, but roar instead.
- Tabby cat taking a cat nap on a pair of shoes image by mario beauregard from Fotolia.com
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