In one of the first scenes of the movie, the MIT professor is lecturing and turns to write the homework assignment on the chalkboard. The board is two boards wide and two boards high. The top and bottom boards can be switched by pushing the lower board up and the upper board comes down. The professor lifts the lower board so that he can write the assignment on the bottom of the lower board without having to bend over. When he is done, he pushes the board back down. A minute or so later when the camera shot changes to another angle the lower board is seen pushed up halfway. Next shot: board down. Next shot: board up.