The Cressi Shock Cord is a must have for spear fisherman. This invaluable cord can save you the frustration of losing your catch, your shaft, or breaking your line. One end attaches to your gun and the other to your line. The concept is that tension is dampened, more so than just attaching your line directly to the gun. This is advantageous when your catch pulls on the line; instead of the shaft tearing out of your catch, the shock cord offers less resistance on the line. Don t go spearfishing without a shock cord, or you might lose your catch!