A cat's purr is one of his most unique characteristics. Exactly how a cat produces the sound is a matter of conjecture. One theory is that the sound is caused by turbulence ihn major blood vessels during inhalation and exhalation.
Another is that it is produced by vibrations of the soft palate. The most likely explanation is that the sound arises in the voice box from tensing of the vocal cords which vibrate as the cat breathes in and out.
Purring is an instinctual act. Kittens purr as early as two days of age. A common misconception about purring is that it always indicates a state of pleasure. In fact, cats also purr when they are hungry,upset, or in pain. Cats have been known to purr just before dying.
