Nine lives are sound-based...

Slashdot recently featured a blurb referencing an article in The Daily Telegraph that discusses how cats "heal themselves" by purring. It's a rather interesting article that touches on the benefits of exposure to low-frequency sound for both felines and humans. It doesn't talk about HOW cats purr, however, so if you're looking for that you'll have to hit the vet texts. The article also references some of the extraordinary accidents that cats have been involved in and survived (for example a 45-story fall).