After Gwen leaves Gerald's room, he writes a note and tucks it into the flap of the desk pad calendar. After he is killed and the nurse finds the note, it is now out in the open in the center of the desk.
Near the end, when they're all standing in the room with the rigged door latch, the actors' positions change from shot to shot.
When the maid screams after seeing rats, a male's moaning sound can be heard immediately after. But the moaning sound didn't come from any of the actors, so it apparently was an off-screen voice from a crew member.
When Hubert is in his room, a gunshot is heard and Hubert ducks down easily and looks to the rear of the room as if the bullet missed. But there was only one gunshot, and on the next cut, he is shown holding on to his chest area as if he's been hit.
Brucker's writing of the safe numbers taken off the toupee in Aunt Lucy's room doesn't match the actual amount of numbers shown on the paper when he is opening the safe.
When Gwen is sitting down in Gerald's room with her back to the window, there is a man with a gun outside the window looking in. As she gets up, the man hides. She then exits through the window, which is the same way she entered. The man had no way of knowing that Gwen was leaving and that she entered through the window and was going to exit the same way; therefore, he had no reason to go hide at that precise moment.