To the disappointment of gangster's heavies everywhere, cracking your knuckles does not actually crack your knuckles. Researchers used an MRI to record in real time what actually happens when you "crack" joints (I'm sure this has important scientific relevance and is in no way a waste of valuable medical resources.) Joints are lubricated by synovial fluid: separating them results in "the rapid creation of a gas-filled cavity" and a distinctive popping sound. But the joints themselves remain stubbornly uncracked.
The not at all frivolous-sounding research on "Real-Time Visualization of Joint Cavitation" was conducted last year and provides "a new theoretical framework to investigate health outcomes associated with joint cracking." To be honest, the only health outcomes associated with joint cracking that I am aware of are increased levels of stress among people who owe large amounts of money to loan sharks. I await similar scientific research that will no doubt be of interest to burly men with names like Fingers, Nails, Smiley, and Johnny No Nose.
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