A venomous snake (family Viperidae) in which the tip of the tail consists of interlocked segments of keratin forming a rattle that the snake vibrates to deter and warn potential aggressors. They are pit vipers, with facial organs that detect the body warmth of prey, and they have a keen sense of smell. Rattlesnakes occur throughout most of North, Central, and South America in most types of habitat. There are two genera with 36 species.