Scientific American answers: Why do cats purr?

Scientists have demonstrated that cats produce the purr through intermittent signaling of the laryngeal and diaphragmatic muscles. Cats purr during both inhalation and exhalation with a consistent pattern and frequency between 25 and 150 Hertz. Various investigators have shown that sound frequencies in this range can improve bone density and promote healing.

We have 4 of these creatures. Go ahead, break our bones! We’ll be healed in a week.

Stolen from Fark.