feeding doesn't ALWAYS mean healthy oreo. Some snakes will eat no matter what.
As far as your snakes behavoir, its seems like you just have a shy snake. Younger snakes are very skittish and shy. Just about everything is a predator to them when they are that age, even you. Some will respond aggressively (rattling tail, striking, etc) and some will just try to disappear by hiding or staying still. I would guess that yours is the shy kind. The reason he hid his head is because thats the most vital piece of his body, and he didn't want that exposed. How long have you had him? Give him a period to adjust and get out of his baby stage and he'll be fine.
Amy is also correct. Before you introduce anything new into your viv especially something that you found on a walk or hike, for the safety of your snake, bake it at about 275-300 degrees frist to kill al bacteria and nasties on it. There are a few types of trees that are toxic to younger corns such as pine and cedar, so try to avoid any twigs from them