Escaping gases: Scientists explain that synovial fluid present in your joints acts as a lubricant. The fluid contains the gases oxygen, nitrogen, and carbon dioxide. When you pop or crack a joint, you stretch the joint capsule. Gas is rapidly released, which forms bubbles.
本身fluid入面就有氣體 (水都有咁解)咁你啪果下去到extreme range = decrease joint space = increase air pressure 咪爆