The naderos is found in some medieval encyclopedias. It is a serpent that can infect both living animals and inanimate objects with its poison. If a freshly-cut branch is touched to the serpent's mouth, the bark on the branch witl blister and bubble. If the serpent's tongue touches the tip of a sword, the poison will run up the blade, turning it blue as though a flame had burned it. If a man is struck in the foot, the poison will move up his leg until it reaches the heart, when he will die. The serpent can be warded off with an ointment of rue or wormwood applied to the hands and feet.