[LarryMullins]

> The sound of cracking knuckles is actually a release of gas in the joint

That's only partially correct at best, because joint cracking is not a single phenomenon. For one, there is disagreement over whether the sound comes from the formation of the gas bubble, or the collapse of the gas bubble (cavitation). It is likely that both are partially true.

Furthermore, it doesn't explain the sort of joint cracking in which people can crack a joint repeatedly with no cooldown. I can crack my wrists and ankles by twisting my hands and feet around in circles, cracking once per rotation as fast as I can turn them around. 60 cracks a minute easily; neither of the gas bubble hypothesis can explain this, it is almost certainly a matter of ligaments or bones moving around against each other in a way that creates a snap sound, like snapping your fingers makes a crack sound by slapping your middle finger against the base of your thumb.