Scientists find why knuckle-cracking makes noise

Scientists from Paris' Ecole Polytechnique and Stanford University in the United States have found that the sound when you crack the knuckles is caused by the ‘partial’ collapse of microscopic bubbles of joint fluid in the hand.

Abdul Barakat, a professor at the Ecole Polytechnique, was quoted as saying, “It could be multiple bubbles, but we showed that the collapse of a single bubble is sufficient to give you the signature sound you get.”