Heroes to creatures of habit everywhere, researchers at the University of Alberta recently endeavored to investigate the physiology behind knuckle cracking. In an experiment that no one had ever bothered to do before, they performed an MRI of seasoned knuckle cracker (and chiropractor) Jerome Fryer in action.
Analysis of the imagery revealed that the sound actually comes from the rapid separation of the bones, which in turn creates a bubble of gas in the fluid that lubricates your joints. Its the formation of this bubblenot the subsequent poppingthat causes the sound we know so well.
While their conclusion may do little for the general gross factor of knuckle cracking, it does suggest that the habit is pretty harmless. Still, it may be one worth breaking if you find yourself going on a lot of first dates or job interviewsand not so many second ones.