Venom is a secretion containing one or more toxins produced by an animal to cause harm to another. Venom has evolved in a wide variety of animals, both predators and prey, and both vertebrates and invertebrates.
Venoms kill through the action of at least four major classes of toxin, namely necrotoxins and cytotoxins, which kill cells; neurotoxins, which affect nervous systems; myotoxins, which damage muscles.
Venomous animals kill tens of thousands of humans per year. However, the toxins in many venoms have potential to treat a wide range of diseases.