the snake is not to be trusted. it is unknown to us, so we are suspicious of it (as we should be). we are suspicious of all things that are unknown to us, including knowledge - which can lead us into dark and dangerous places.
sometimes we must submit to its bite. - it is only by taking it into us that we can become conscious, or understand its meaning.
the snake is one of the most common symbols of transcendence. the idea of going from one form to another is presented in a most direct way when we see it shed its skin.