Crangon (Alpheus) and Synalpheus are the two principal genera of noise-producing shrimp. These animals (not to be confused with commercial shrimp, which are noiseless) are about 3/4 inch to 1-1/2 inches long. They have one enlarged claw which produces a vigorous snap when closed. Over a large colony there is a continuous succession of snaps which causes an intense crackling noise resembling the burning of dry twigs. With increasing distance from the shrimp bed, the crackle merges into a sizzle or a hiss.