Revealing mistake: When the camera is tracking in to Peter Lorre whistling in the cafe, part of the screen gets noticeably darker because the camera is blocking one of the lights. This happens in other scenes, noticeably, when the camera makes shadows.
Continuity mistake: After Elsie has been kidnapped, there is a scene where a little girl walks up to an old man to ask him for the time. A man notices this and walks towards the old man. The old man is standing in front of a light pole which casts a shadow onto the pavement. In another shot, there are no shadows near the light pole.
