poisonous New World snake of the pit viper family, distinguished by a rattle at the end of the tail. The head is triangular, being widened at the base. The rattle is a series of dried, hollow segments of skin, which, when shaken, make a whirring sound. When the snake is alarmed, it shakes its tail, and the noise serves as a warning to the attacker. While the snake is young, three or four segments are usually added each year, one at each molt. After maturity fewer develop and old ones start to break off. Rattlesnakes feed on rodents, birds, and other warm-blooded animals. Like other pit vipers, they have heat-sensitive organs in pits on the sides of the head, which help them locate and strike at their prey. The erectile fangs are folded back in the mouth, except when the snake strikes. The venom is highly toxic to humans and occasionally proves fatal (see snakebite ). Rattlesnakes bear live young. Most species are classified in the genus Crotalus. The timber rattlesnake, C. horridus , …