Venom is actively injected, while poison must be eaten or absorbed. So snakes and spiders have venom, because they typically use fangs to inject it into their victims. Some frogs, however, have poison, because one must touch their skin to absorb it. No one knows for sure, because there are at least 35,000 kinds of spiders. So far, however, less than 100 are known to be a threat to people, although many others can easily poison their prey.
Some animals advertise their toxicity.
The toxicity of some snake venoms, for instance, changes as the snake ages, or depends on what it has been eating. Similarly, the deadliness of snake and spider venom can vary from place to place in the same species. In general, however, the bite or sting of the deadliest animals can cause an adult human being to die within 15 minutes, usually by destroying the brain's ability to send the signals that allow us to breathe. Paralyzed, we suffocate. By advertising their toxicity, an animal may avoid attack.