The rattlesnake is any of a kind of venomous snake belonging to the genera Crotalus and Sistrurus, widely distributed in the dry desert regions of the United States and Mexico. Its name derives from the interlocked keratin-ringed rattle which they have at the end of their tail, producing a buzzing sound when shaken. The Mojave rattlesnake (Crotalus scutulatus) has a heart-shaped head with vertically-elongated pupils, and an average bodily length of 1 m (3ft4in); it has brown and creamy white scales that form diamond patterns on its back. The Mojave rattlesnake has neurotoxic venom, which distinguishes it from other rattlesnakes that has hemotoxic venom. Its neurotoxin affects the nervous system, especially the nerve cell transmission, provoking muscle paralysis.