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At the heart of joint cracking lies synovial fluid, a magical lubricant that bathes our joints. Containing dissolved gases like carbon dioxide and nitrogen, synovial fluid creates an environment where joint movement can produce that signature popping sound.
Stretching the joints apart increases the space between the joints, which decreases the pressure in the joint capsule. This creates a vacuum that fills with gas from the synovial fluid, forming bubbles. When the bubbles burst, they make the popping sound.