Snakes are long, thin, legless reptiles. Most live in warmer regions, but some adders live inside the Arctic Circle. With no legs to grasp victims, snakes kill their prey in other ways. Constrictors such as pythons wrap themselves around the animal and stop it breathing. The venom is made in special salivary glands and injected into victims through fangs - though a few snakes can spit venom.
Snakes hunt their prey by sight, sound or smell.
They have no ears, but pick up sound vibrations from the ground. They smell with their tongue, which picks up minute particles floating in the air as it flickers in and out. The boa constrictor kills its victims by squeezing them until they suffocate. Boas grow up to 5.5m long, but some constrictors are even bigger. The anaconda of America is up to 11m long.