Scientists know that game fish are attracted to certain sound waves. That?s 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.