Not all snakes are venomous, but even nonvenomous snakes are subject to strike if they feel frightened or sense danger. In North America, an easy way to determine if a snake is poisonous is to look at its pupils. With the exception of the coral snake, the pupils of poisonous snakes are elliptical or slit-like, much like the eyes of a cat, while the pupils of a non-venomous snake are round.
There are a variety of snakes in the U.S., but only four are venomous, including the rattlesnake, copperhead, cottonmouth and coral snake. According to the U.S. Centers for Disease Control (CDC), as many as 8,000 people are bitten by poisonous snakes each year, although only around five die.