Revealing mistake: In the final scene where Miss O'Shaughnessy is in the elevator with the detective, the door closes and the elevator starts to 'descend', indicated by dark glass going down, supposedly because the lighted elevator is passing beyond the view of the exterior door. But if you look, you can still see the silhouette of Miss O'Shaughnessy behind the glass, not moving. It is just a piece of wood or something being lowered behind the glass to simulate the elevator going down.
Revealing mistake: In the last scene when O'Shaughnessy is being taken down in the elevator, one can tell that the elevator is not descending: rather something opaque is being lowered (like a window shade) to make appear as if it is descending. If you look closely through the translucent outer elevator door both the scissor-door pattern of the interior cab gate and the outline of O'Shaughnessy's torso remain stationary and don't descend.
