A reptile possessing scales and lacking limbs, external ears, and functional eyelids. In poisonous snakes, venom is produced in a poison gland, which is connected by a tube or groove to a poison fang, one of two sharp elongated teeth present in the upper jaw. In the U.S., the coral snake, copperhead, water moccasin (cottonmouth), and rattlesnake, of which there are 15 species, are poisonous. All except the coral snake belong to the pit viper group, because they possess a sensory pit between the eye and nostril.