We examine our patients for any obstructions in the spine or joints. When joints are obstructed, that means they do not move as they are supposed to move. We free these joints. Freeing the joints is often done using thrusting techniques with the hand. As a result, air will escape from the joints. This escape of air is often accompanied by an audible crack. This can be compared to the cracking sound that is made when you pull your finger quickly.