Continuity mistake: In the last scene to be filmed, with Orlock and Gretta, the candles on the dresser are alternately lit and then out, as Orlock's reflection is visible then not in the mirror.
Factual error: After a new camera man is hired, Wagner, the camera man starts showing off to his fellow crew members that he invented "slow motion". In the next scene he demonstrates this by spinning the handle of the camera slowly. In fact this is not right, when the movie is projected the movie will be speeded up instead of slowed down.
Continuity mistake: In the scene where Gustav and Count Orlock are discussing the real estate contract, the locket that falls out of the bag first shows a photo of Greta, but in the next shot, it is a painting that looks completely different.
Continuity mistake: In an early scene FW Murnau is talking to his leading lady after a scene was filmed and her cigarette ash moves from very long to short and back and forth throughout the scene.
Continuity mistake: When Fritz Wagner arrives on the scene in the airplane, it seems to be close to dusk, still light out. The scene he is walking to is pitch black. When the camera cuts from Fritz to the scene to be filmed, this light/dark problem continues until he reaches the camera.