When Norman hides in the classroom "I Do Not Believe" is written on the chalk board with other key words related to witchcraft. Something off screen appears to him and he backs up to the chalkboard in fear. After the PA system is silenced, he walks back to the door. The blackboard has been smudged, creatively revealing the phrase "I Do...Believe"
The trivia item below may give away important plot points.
The shot of the eagle bursting through the door was achieved by punching a glove puppet through a miniature of the door. There are only a few frames of this sequence before a very quick cut to a shot of an actual eagle in a miniature of the hallway, but the shape of a hand and wrist can just be made out in silhouette.