A species of African rat makes its own poison by gnawing on a toxic tree and smearing the toxic saliva on to hair on its flanks. The Crested Rat, Lophiomys imhausi, is the first mammal ever found to acquire lethal toxins from a plant.
The poison comes from the Acokanthera tree, and has been harvested by human hunters to coat arrows that can kill an elephant.
Read more at University of Oxford