Snakes do not normally prey on humans, but there are instances
of small children being eaten by large constrictors in the jungle.
While some particularly aggressive species exist, most will not
attack humans unless startled or injured, preferring instead to
avoid contact. In fact, most snakes are non-venomous or have venom
that is not harmful to humans.
The skin is covered
in scales. Most snakes use specialized belly scales to move, gripping
surfaces. The body scales may be smooth, keeled, or granular.
Their eyelids are transparent "spectacle" scales which
remain permanently closed. 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. In "advanced" (Caenophidian)
snakes, the broad belly scales and rows of dorsal scales correspond
to the vertebrae, allowing scientists to count the vertebrae without
dissection While snake vision is unremarkable (generally being
best in arboreal species and worst in burrowing species), it is
able to detect movement. In addition to their eyes, some snakes
(pit vipers, pythons, and some boas) have infrared sensitive receptors
in deep grooves between the nostril and eye which allow them to
"see" the radiated heat. As snakes have no external
ears, hearing is restricted to the sensing of vibrations, but
this sense is extremely well developed. A snake smells by using
its forked tongue to collect airborne particles then passing them
to the Jacobson's organ in the mouth for examination. The fork
in the tongue gives the snake a sort of directional sense of smell.
Above Images Are From The US Fish & Wildlife Service