The snakes or serpents are legless reptiles, some of which have a venomous bite which they use to kill their prey before eating it. Other snakes kill their prey by constriction, for example strangulation.
Snakes are closely related to lizards, which share the order Squamata. There are also several species of legless lizard which superficially resemble snakes, but are not otherwise related to them.
Although they may be venomous and have a bad reputation, snakes do not prey on humans. Most snakes will attack a human being only if startled or injured. If you look where you are walking and make plenty of noise, a snake will get out of your way rather than waiting for you to step on it. In many areas, most snakes are non-venomous or have venom that is not harmful to humans, and are Colubrid. Australia is an exception - most snakes in Australia are extremely venomous and should be given a very wide berth.
All snakes are carnivorous, eating small animals, birds or insects. Snakes do not chew their food. Snakes have very flexible lower jaws, the two halves of which are not rigidly attached, allowing them to open their mouths wide enough to swallow their prey whole, even if it is larger in diameter than the snake itself. Contrary to the popular myth, at no point do they "unhinge" their jaws (disarticulate their mandibular joints). After eating, snakes become torpid while the process of digestion takes place.
The skin is covered in scales. Most snakes use specialized belly scales to move, gripping surfaces. Their eyelids are permanently closed but transparent "spectacle" scales. They shed their skin periodically. Unlike other reptiles, this is done in one piece, like pulling off a sock. It is thought that the primary purpose of this is to remove external parasites. This periodic renewal has led to the snake being a symbol of healing and medicine, as pictured in the Rod of Asclepius
Detailed vision is limited, but does not prevent detection of movement. A subgroup of snakes called the pit vipers have infrared sensitive receptors in deep grooves between the nostril and eye which allow them to 'see' the heat radiated by animals. Hearing is restricted to the sensing of ground vibrations, as snakes have no external ears. A snake smells through its nose, and the tongue passes airborne particles to the Jacobson's organ in the mouth for examination. The left lung is very small or sometimes even absent, as snakes' tubular bodies require all of their organs to be long and thin, and to accommodate them all only one lung is functional.
Web link: http://www.embl-heidelberg.de/~uetz/families/taxa.html.
Some of the constellations of the sky are symbolised after snakes. Serpens represents a snake being tamed by the snake-handler Ophiuchus. Hydra is the many-headed serpent killed by Heracles. Hydrus, the water snake, is a minor southern constellation.
Snake is considered as a symbol of evil in Christianity.
The Snake is one of the 12-year cycle of animals which appear in the Chinese zodiac related to the Chinese calendar. It is thought that each animal in the Chinese zodiac is associated with certain personality traits. See: Snake (Zodiac).