VIPER

Characterized by a pair of long, hollow fangs, usually with reserve fangs beside them, in the front of the upper jaw. The fangs fold back against the palate when not in use and quickly swing forward to strike, injecting a deadly venom that attacks blood and tissues.
The viper’s broad, triangular head is generally covered with scales, and the eye has a vertical pupil.
They are distributed worldwide, with most found in Africa.
Pit vipers : have deep pits containing heat receptors on each side of the head between the eye and the nostril that enable the snakes to detect warm-blooded prey in the dark.

There are more than 120 species.
Important ones are rattlesnake, moccasin, copperhead, fer-de-lance, and bushmaster. Most inhabit the western hemisphere; a few are native to Asia.