the.com/purr
a cat's low-frequency hum that may literally help mend its own bones
healing rangeVibrates at 25-150 Hz, frequencies known to aid bone density
not just joyCats also purr when injured, stressed, or dying
silent trickCheetahs purr, but lions and tigers cannot
built-in motorPowered by rapid twitches of the larynx muscles
human requestSome purrs hide a cry mimicking a hungry baby