rubbing head on door

When I let my snake out in my room and he goes under my door, he often times rubs his head up against the bottom of the door. It's not a tight squeeze or anything, about 1-2" tall for a baby ball. He actually lifts his head up to rub it on the door. Is this unusual, and what causes it? Thanks for the help!

He is probably trying to take cover... baby ball pythons don't really care for open spaces (like the floor of a room) too much....very very stressful on the bp.