Why do cats purr?

Someone ask: Why do cats purr?

Cats purr for few reasons, and science tribe still argue on some parts. Often purr happen when cat feel safe, sleepy, or happy, like small fire humming in warm cave. But cat also purr when hurt, scared, or sick, so purr not only joy song. Likely, brain send steady signal to voice box and chest muscles, making air and tissues vibrate in throat. That vibration may soothe cat, and maybe help bone and tissue heal by gentle shaking. Kitten purr to guide mother, and mother purr back like tribe drum saying “here, safe.” Cave wisdom: purr is not one message, but many messages in one soft rumble.