Several snakes species from the elapid family posess the ability to "spit" their venom, propelling it through the air. These species can be categorized into three groups, two of which are African, and one Asian. The foremost members of each of these groups are:
Like all other elapids, spitting cobras have hollow fangs that are fixed in place. During a bite, the venom glands contract, and venom is forced out of a small hole in the end, into the victim. The venom hole is smaller for spitting cobras, to allow pressure build up, and on the front of the fang, although still near the bottom. To spit venom the snake contracts its venom glands while blowing out air. This results in two fine streams of venom that may be aimed accurately at up to 8 feet for larger snakes.
Spitting is not used to catch prey, instead it is a purely defensive tactic. Spitting is often preceded by the snake rearing up, and spreading its hood, but spitting cobras are just as able to spit from a prone position if startled. The target of the venom is the aggressor's eyes. The venom causes a very painful smarting, and induces temporary blindness, which may be permanent if the dose was large, and the venom remains on the conjunctiva for too long.
Humans who have been spat at should slowly retreat, and then attempt to wash the venom from their eyes. Thankfully, the likelihood of a follow-up strike is small. Milk is the best substance with which to wash the eyes out, but water will do fine, and urine is acceptable in an emergency (as most of these cases are).