Other mistake: When Jennifer and Gary are scratching the messages to each other on the painted glass, the glass is painted black on both sides so they wouldn't be able to see each others scratchings as the paint on their side would cover the marks the other was making.
Continuity mistake: During the scene when Jennifer gets matches on her side of the room, she lights one, presumably to see into the other room. In one shot the match is burned down almost to her finger, the next shot from the other side of the glass it is longer, and the next shot shows the match at a different angle with a larger flame than the previous shot. When she drops the match because it is supposed to have burned to her finger, it is clear the flame was not close to her finger/thumb at all.
