Cat Purr

Cats purr while they are content and happy or when they are under stress, when the purr acts as a "mantra" (a self-soothing, self-healing, relaxing, vibrating sound). Maybe a little bit like the "Om" one might hum in the lotus position. It has been found that sound frequency in the range of your average purr can stimulate bone growth and healing. Cats are often used as "therapy animals" in convalescent hospitals or retirement homes.