This beautiful mushroom’s colors are a sign to stay away. It produces a poison that will sicken people unless it is cooked very thoroughly.

In most uses, this word refers to something that can harm or kill an organism. But in biology, only some organisms that make a toxic substance are considered truly poisonous. To get that name, they must secrete the chemical passively. Then it just stays on or inside the organism until somebody — or something — eats it. Plants can be poisonous. So can animals that secrete toxins through their skin. But if an animal has to bite or sting to deliver its toxic chemical, scientists call it something different: venomous.