When Sutherland witnesses the murder, it can be clearly seen, though in shadow, that the murder weapon is a revolver. Later however, when Sutherland is shown the murder weapon in the police station, the weapon is a semi-automatic, and not a revolver.
When Donald and Mary are seen together in bed eating chocolate cake, creaking can be heard around them on the floor, though neither of them move. It is most likely sounds made by the crew or cameramen.