Approximately 2500 different species of snakes are known. The frequency of shedding varies with different species , according to the size and age of the individual. Young, rapidly growing snakes shed their skins more frequently than the slow-growing adults. If the venom gets into the eyes, it may cause blindness. The spitting is used only in defense and never to obtain food.
Vision is well developed in most snakes, but many burrowing snakes are virtually blind.
Snakes have a strong sense of smell, which is relied on to a large extent in hunting food. Snakes find their prey by sight and scent, and sometimes temperature. Except for burrowing species, snakes have excellent short-range vision. Snakes are deaf to airborne sounds. The Cobra does not hear, as it is believed, the snake -charmer's flute.