The News Minute | March 29, 2015 | 04:27 pm IST Ever wondered what happens to your knuckles when you crack them? Or how does it affect you?For 60 years, Donald L. Unger cracked the knuckles on just his left hand but not his right hand to show that knuckle cracking did not cause arthiritis. The space between our joints is filled with synovial fluid, which contains several gases including oxygen, nitrogen and carbon di oxide. The fluid helps reduce friction between the joints. A video illustration by Vox attempts to explain the science behind popping ones joints and the sound which is created in the process. Watch the video to know more.