There is good reason to keep your ears pricked for the rattles on the tail of the American rattlesnake. Its bite is spiked with a very powerful cytotoxin.
Cytotoxins, which initiate the digestion of the prey even before it is swallowed, are the most primitive form of venom. The poison destroys cells—especially those in muscles—so they die and tissue collapses. Some types attack specific cardiac muscles, causing heart failure, while others have more widespread effects. Powerful venoms of this type are found in American rattlesnakes, among others. Someone who's been bitten and survives may still end up with disfigured fingers, toes, arms or legs; requiring amputation in severe cases.