It's an Eastern Hognose Snake, Heterodon platyrhinos, a completely harmless bluffer. If the "cobra" act doesn't work to scare off a potential enemy, the snake will writhe about, gasp as if in agony, roll over on its back and "play possum", pretending to be dead, and will stay that way until the threat leaves. They are absolutely harmless and all the hissing, neck-spreading and fake striking is just a bluff; these snakes cannot even be made to bite a human or any animal other than a toad, which is all that they eat.
