Asked by: Steve Shaw, Durham

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A 2015 study at the University of Alberta, Canada took real-time MRI images of finger joints as they cracked. The researchers found that as the surfaces of the cartilage pull away from each other, they create a site for a tiny bubble of dissolved gas (mostly CO2) to form in the joint’s lubricating fluid. The sudden expansion of the bubble creates the popping sound.

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luis villazon
Luis VillazonQ&A expert

Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.

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