One site says this:
snakes are often considered symbols of temptation and evil, anger, and envy. Snakes emerging out of the ground may represent your unconscious or repressed materials coming to your conscious mind. Freud thought that the snake was a phallic symbol. It is amazing how many people have snake dreams! Most snake dreams seem to be disturbing and they leave the dreamer feeling anxious and afraid. There are no simple interpretations to the snake dreams. Each dreamer must consider their own situation and all of the details of the dream. Sometimes snakes may be phallic symbols and other times they represent negativity in our lives that hampers our progress and constantly threatens us. In the long run the snake may be a positive symbol; it may represent difficulties that lead us to the center of personality and result in feelings of completeness.
"Phallic" means "Willy-shaped".
Another site says this:
A snake ready to strike means treachery from one you least expected; killing it means victory over enemies.
Another site says this:
To see a snake or be bitten by one in your dream, signifies hidden fears and worries that are threatening you. Your dream may be alerting you to something in your waking life that you are not aware of or that has not yet surfaced. The snake may also be seen as phallic and thus symbolize dangerous and forbidden sexuality. The snake may also refer to a person around you who is callous, ruthless, and can't be trusted. As a positive symbol, snakes represent transformation, knowledge and wisdom. It is indicative of self-renewal and positive changes.
They're talking about willies again.