Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with many more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads with their highly mobile jaws.
Snakes can be venomous and non-venomous. Venomous snakes have distinct heads. While non-venomous snakes have a rounded head, venomous snakes have a more triangular-shaped head. Examining a snake’s pupils is another method that can be utilized to identify venomous versus non-venomous snakes. Like a cat’s eye, poisonous snakes have thin, black, vertical pupils surrounded by a yellow-green eyeball while non-venomous snakes have rounded pupils. While this type of pupils can indicate that the snake is venomous, this is observed at close range, which can be a potentially dangerous identification method.