It is illegal in the United States to shoot or harm a woodpecker in any way. Snakes are a much maligned creature with many myths surrounding it. One of the most common myths about snakes is that if it has a triangular head, it is poisonous. This is not necessarilly true. Although most poisonous snakes do have triangular heads, this trait cannot be used to determine if a snake is poisonous or not.
Most snakes have the ability to flatten their heads, which gives it a triangular appearance.
This is especially true if the snake is irritated. The only poisonous snake that is commonly found in the Atlanta area is the copperhead. The best way to educate yourself about the different types of snakes found in your yard is to get a local field guide. Snakes play an important role in the natural balance of even a small ecosystem like your yard. Without them, you would probably be overrun with small rodents.