I, too, have read that. Something to do with sounds waves. We used to think that purring meant only happiness, but cats purr when they are injured or sick, too. I think that they purr to get our attention as well as to heal themselves. It does make you feel better listening to it. When I'm sick, Spunky will sit on me and purr away. He insists on it.

Have you heard that cats meow only for us humans? It seems that they have their own methods are communicating with each other. I personally think they are psychic.