It's been a mystery for 3,000 years but the code may have finally been cracked. Researchers say they have discovered why cats purr.

 

That motorized revving that all feline fanciers love isn't, it seems, merely a sign of contentment but rather a seal-healing mechanism that helps the animal's bones and organs to regenerate and grow stronger.

 

Cats purr at a sound frequency of between 27 and 44 hertz, a discovery that reinforces studies that human bones are strengthened when they are exposed to frequencies of 20 to 50 hertz.

 

Most cats - wild and domestic - purr. (Tigers don't.)  Next up is to try to determine the mechanics of the process.  And the secret cats have behind their enigmatic stare could very well help humans.  Some scientists are taking their cue from the cat and studying whether sound therapy can help halt osteoporosis.