The rattlesnake is a kind of snake, a reptile. About 50 kinds of rattlesnakes are known: they are a kind of pit viper. There are two groups of rattlesnakes: the genera) "Crotalus" and "Sistrurus". All have a venomous bite, and some are much more dangerous than others. Pit vipers have a set of heat-sensing "pits" on their faces that help them find prey and move towards it, even in the dark.