A baby snake has no control over the amount of venom delivered by its bite, thus always giving a full dose. A baby cobra is fully able to defend itself in as little as three hours after entering the world. Cobras are completely immune to the venom produced by their species. Thus the poisons secreted by the skin of some toads, or accumulated in the bodies of numerous inedible animals, are ordinarily not considered venoms. The most familiar venomous animals are certain snakes and insects and the spiders and other arachnids.
Venomous species occur throughout the animal kingdom, however, including the mammals.
Some shrews, for example, have venomous saliva, and the platypus bears poison spurs on its hind legs. The severity of a venom's effects depends on several factors, such as its chemical nature, the stinging or biting mechanism involved, the amount of venom delivered, and the size and condition of the victim. Thus, few of them are poisonous to humans, but their venoms are quite effective on insect prey. Chemically, venoms vary greatly across the animal kingdom and are not readily defined. Snake venoms, for example, are complex mixtures of enzymatic proteins and different toxins.