A snake flicks its forked tongue to pick up chemicals from the air, the ground or the water. A snake's sharpest sense is smell. Jacobson's organs are two small organs in the roof of a snake's mouth. Each opens to the mouth through a tiny hole in the palate. After a flick, the snake's tongue goes back into its mouth. It fits into the Jacobson's organ, which sends signals to the same part of the brain as the nose.

Snakes have no eyelids, so they cannot blink. Instead of eyelids, a snake has a clear scale over each eye, called a spectacle or eye cap, that protects it. Snakes shed their old skin as they grow. Just before a snake sheds, its eyes turn cloudy or bluish. Before a snake sheds, a layer of fluid forms between the old skin and the new skin.

Snakes have no outside ears. A snake senses moving prey by feeling vibrations, which it picks up through its jawbones and body. Some snakes have heat-sensing pits on the sides of the head. A snake's pit organ, which sits between the eye and the nostril in rattlesnakes, can sense infrared radiation, which is heat, given off by warm-blooded prey. The pit gives the snake a picture of its surroundings, a thermal image.

Many snakes are ambush hunters. They hide and wait for an animal to come close, instead of chasing it. Rattlesnakes find a hiding spot at dusk and wait to catch mice, ground squirrels or rabbits. A wild snake is best left alone: it will usually go its own way. If one is near a home, a grown-up can call animal control.

Snakes are cold-blooded: their body temperature depends on the temperature around them. Snakes warm their bodies by lying in the sun. In cold weather snakes rest through the winter in a state called brumation, which is like hibernation. Garter snakes usually spend the winter together in groups, and they are among the first snakes to wake up in spring.

Words to know

• forked: split in two
• chemicals: tiny substances
• vibrations: tiny shakes
• infrared: unseen heat
• thermal: made from heat