The Snake Simile is a teaching by the Buddha also known as Alagaddupama Sutta. The main concern of this discourse is to warn against misconceptions and dilution of the teachings Buddha revealed to his students. While the Buddha repeatedly stressed that his Teaching should be accepted only after due investigation, and uninfluenced by tradition or external authority; while he also advised his monks to make light of praise and blame of the Teaching uttered by outsiders, he was quite firm, and even stern, when misrepresentations of the Teaching occurred on the part of his monks — that is, by those who had accepted the Teaching and had chosen a life devoted to its realization. In The Snake Simile The Buddha for example clarifies concepts such as impermanence and not-self. Download The Snake Simile translated by Nyanaponika Thera here: (45 pages/520Kb):

The Discourse on the Snake Simile