Scientists know that game fish are attracted to certain sound waves. Thats why these unique rattles are so popular with offshore fishermen. They contain a single large ball bearing inside a tuned chamber of luminescent plastic that puts out a distinct click as it rolls from one side to the other. No shark or swordfish rig is complete without one- and even marlin and tuna fishermen are using them. Charge them under a light source and they glow in the dark.