In some households, cracking your knuckles is a declaration of war. For more than 50 years people have been publishing scholarly papers about what is going on in your finger as you pull it. Where the two bones of the finger meet, a little lake of synovial fluid keeps them from grinding on each other. This is the result, Dr. Kawchuk and colleagues wrote, of the formation a bubble, which persisted for some time afterward, and whose creation might be responsible for the cracking noise. They posited that the bubble generated a pressure wave in the fluid, producing a sound.

Source: New York Times March 29, 2018 15:30 UTC