Radiologists may have figured out why knuckles crack and the good news is that there seems to be no harm to your hands when it happens. Via ultrasound readings of people cracking their knuckles, researchers at the University of California-Davis found that the movement shows as a bright flash that comes from a gas bubble forming in the joint.

According to HealthDay, researchers have debated, for some time now, whether the knuckle cracking sound comes from a gas bubble forming or popping in the joint. The ultrasound data, which was presented at the Radiological Society of North American annual meeting, shows the sound is actually caused by the gas bubble formation.

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