Some species of
felines make a sound
which is called a purr. It varies in detail from cat to cat
(e.g., loudness, tone, etc.), and from species to species, but can be
characterized as a sort of tonal buzzing. Some cats purr so strongly
that their entire body vibrates. Cats purr at 27 - 44
How felines purr
Cats produce the purring noise by vibrating their
voice box, in a particular manner. They have a timing mechanism in the brain
which sends neural messages to a muscle in the larynx, rhythmically opening and
closing the air passage several times per second. Combined with the steady
inhalation and exhalation of air as the cat breathes, a purring noise is
Cats can either purr or
roar, one exception being the tigers which can purr but only in one direction.
In general, small cat species purr, while larger ones roar, although pumas and
and do not roar.
One theory held involved
blood hitting the aorta. Another
held that purring might have been caused by the vibrations of the hyoid
apparatus, a series of small bones connecting the skull and the larynx that
nominally serves to support the tongue. Yet another theory held that cats might
possess a special purring organ, though none was found.
Why felines purr
Humans usually interpret the purring of a domestic cat as an expression of
some type of friendliness or contentment. This assumption is based on the
observation that cats often (though not always) purr when being stroked by
humans, combined with the experience that human
children tend to enjoy stroking by their parents and interpret it as a gesture
of affection. Consequently, most humans enjoy listening to or holding a purring cat.
It is, however, not entirely clear to scientists whether this really is one
of the cat's reasons for making the sound; it is well established that a cat
also purrs when it is uneasy, nervous or in great
pain, perhaps to
comfort itself or to express submission. Other theories suggest that a cat purrs
when it wants, needs, or is receiving attention, whether it be affection or
medical treatment. Purring may also reduce pain, help a wounded cat to heal, or
even help to keep a cat's bones strong.
Ethologist Paul Leyhousen, in his book Cat Behavior, interprets
purring as a signal meaning "I am not a threat" to explain the otherwise
differing circumstances that elicit the sound.
Other examples of purring
It is not clear quite how and when purring is used between cats themselves,
which is probably a more important issue bearing on its primary purpose than how
and why it happens when humans are involved. One speculation is that it is a
signalling mechanism between mother cat and
Female cats are known to purr while giving
birth, and this
may be to reduce the pain and also assist post-natal healing. Kittens purr while
nursing, presumably as an "all's well" signal to their mother.
Some cats seem to be able to meow without interrupting the purring sound.