Revealing mistake: There is a large painted hanging cloth backdrop of clouds in the mountain scenes near the end of the film. Vertical streaks can be seen in the backdrop that are the pleats in the fabric. These streaks really stand out in the restored versions of the film.
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.
Revealing mistake: In several of the sanatorium scenes, you can see large pieces of cardboard attached to the lamps to affect the lighting.