Why the cat's purr is one of zoology's greatest mysteries

It's probably one of the most comforting sounds in the world if you like cats. A purr feels like the essence of contentment, but it also sounds downright weird. How do cats make this perfect vibration sound for minutes on end? After decades of study, nobody knows for sure. But there are a few things we do know about… » 8/13/12 10:48am 8/13/12 10:48am