or cottonmouth
Either of two species of pit viper that inhabits marshy lowlands of the southeastern U.S. and Mexico.
The U.S. species ( Agkistrodon piscivorus ) is called a cottonmouth because it threatens with the mouth open, showing the white interior. It is up to 5 ft (1.5 m) long and is completely black or brown with darker crossbands. A dangerous snake with a potentially lethal bite, it tends to stand its ground or move slowly away when alarmed. It will eat almost any small animal, including turtles, fishes, and birds. See also copperhead .