Rattlesnakes are known for the rattles on their tails; these are made from the same material as human fingernails. They have heat-sensing pits on the sides of their heads that they use to locate prey, and young rattlesnakes are independent of their mother within minutes of birth.
Rattlesnakes' rattles are composed of keratin, a hard protein that is also found in hair and callused skin. The sound rattlesnakes make is generated when these rings of keratin are vibrated against one another. Snakes use this sound to warn off predators. Predators that do not flee may be bitten with the rattlesnakes sharp fangs and injected with venom. Rattlesnake bites are not usually fatal to people, as long as proper medical treatment is received following a bite.
Rattlesnakes breed during the spring, and the young snakes develop in egg sacs inside the female snake's body for about 90 days. Rattlesnakes do not lay eggs. Rather, their young emerge encased in thin, membrane-like sacs. Baby rattle snakes are as venomous as adult snakes, if not more so. They shed their skins for the first time when they are about a week old, and at this time their rattles are revealed. Each time a snake grows and sheds its skin, the rattle becomes larger. However, it is a myth that one can tell the age of a rattlesnake from the size of its rattle, since pieces may break off as the snake ages.