Pacific gopher snakes (Pituophis catenifer catenifer) get real defensive when they feel threatened. They basically behave like rattlesnakes, flattening their head, coiling back, striking a lot, and vibrating the tip of their tail, which makes a rattling noise against dry leaves. They make a loud, aggressive hiss. I'm not sure, but they may have some kind of anticoagulent in their saliva, because their bites tend to bleed a lot. Something to investigate...