> Reptiles, immortal like others who shed their skin or bark and thus rejuvenate, are contrasted with mortal men and/or are considered responsible for originating death, perhaps by their bite. In this context, a person in a desperate situation gets to see how a snake or other small animal revives or cures itself or other animals. The person uses the same remedy and succeeds.

Interesting. In the epic of gilgamesh (one of the oldest tales preserved in written form) it is the protagonist who seeks immortality and then has the plant which is supposed to grant it stolen by a snake which then sheds its skin.