The defensive chemicals that poisonous frogs use are alkaloids, a type of compound manufactured primarily by plants. We eat plenty of alkaloids as well, including theobromine (from chocolate) and caffeine (from coffee); we also use many of them as drugs, such as nicotine (from tobacco plants) and morphine (from poppies). In large enough quantities, alkaloids can be lethal. At lower concentrations, alkaloids alter how our nervous system works, by changing our awareness, attentiveness, or alertness. Like frogs, humans also vary in their ability to process and resist the effects of alkaloids. For example, some people are extremely sensitive to caffeine because they do not efficiently metabolize it.

Humans also use certain alkaloids and other neurotoxins as insecticides. Just like poisonous animals resist their own poisons, insects can evolve resistance to insecticides. This is an active area of research for scientists that work in agriculture.

Many poisonous animals have bright colors to ward off their enemies. Together with chemical defense this anti-predator approach is known as aposematism. Colorful markings help potential predators recognize risky prey and prevents experienced predators from making the same mistake twice. Check out these videos of aposematic animals.

The golden poison frog (Phyllobates terribilis) is potentially the most toxic animal in the world—at least for its small size. Some indigenous groups in Colombia continue to use the frog's secretions to poison their hunting darts.

The cone snail is another famous poisonous animal. Watch a video of it harpooning its fish prey here.

Snakes may be menacing predators, but the mongoose resists even the king cobra's venom. Watch them face off here.

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