For cat lovers, there are few sounds as precious as a beloved feline's purr. The purr — which is produced through intermittent signaling of the laryngeal and diaphragmatic muscles — is often interpreted as a sign of contentment, but the real reasons for this vocalization are a bit more complicated.
First of all, not all purring indicates pleasure. Cats also purr when they are nervous or in pain, leading some experts to believe that this uniquely feline vocalization is actually a method of self-healing.
A domestic cat's purr has a frequency of between 25 and 150 Hertz, which happens to be the frequency at which muscles and bones best grow and repair themselves. It is, therefore, speculated that cats naturally evolved their purr over time as a survival tactic — a biomechanical healing mechanism that ensured speedier recoveries.
Of course, cats purr even when they aren't injured. Many domestic cats purr to indicate hunger, for example. A recent study out of the U.K. shows that some cats have even developed a special purr to ask their owners for food. This "solicitous purr" incorporates cries with similar frequencies as those of human babies. These conniving kitties have tapped into their owners' psyches — all for more kibble.
And a cat's purr, like their meow, is also a form of communication. A mother cat teaches her kittens to purr when they are just a few days old. This helps the deaf and blind newborns locate their mother more easily, and may also serve as an early bonding mechanism.
But even the experts concede that, sometimes, a purr is just a purr. One veterinarian — Kelly Morgan of the University of Illinois at Urbana-Champaign College of Veterinary Medicine — likens the purr to the human smile.
"People will smile when they're nervous, when they want something and when they're happy, so perhaps the purr can also be an appeasing gesture," Morgan told WedMD.