10. Poison Dart Frogs These tiny rainforest dwellers measure only 1 to 6 centimeters, yet some species carry potent skin toxins that can sicken or kill adults. Their bright colors warn predators and curious humans alike, a natural sign that danger lurks just beneath the surface. The toxins vary by species and have historically been used by indigenous peoples for hunting, though today accidental contact can cause numbness, paralysis, or, in rare cases, death. Most incidents involve children or people who handle the frogs or get toxin on wounds. Habitat loss and pollution threaten these frogs, while researchers stress the importance of avoiding interaction in the wild.