After having worked at the machine for ten hours, Freder is clearly exhausted when he enters the catacombs and goes down the last stairwell. When he relieved Georgy (worker 11811) earlier in the film, Georgy was sweating--implying Freder should now be sweating too. However, when he takes off his beanie in the catacombs, his hair isn't wet from sweat at all.
When Fredersen and Rotwang leave Rotwang's laboratory to observe Maria's secret meeting, they descend a spiral staircase that spirals clockwise. When they reach the bottom of the stairs, they are seen descending a spiral staircase that spirals counterclockwise. This is repeated when Freder uses the same staircase later in the film.
(This could very well be the result of editing: the footage could have been reversed by mistake. This was the case in some of Lawrence of Arabia's footage of the desert panoramas where a whole reel was reversed.)
On the Kino DVD, this is a dark scene in chapter 15. The brightness setting has to be turned up to catch this mistake. Rotwang is escorting Joh Fredersen to the catacombs. He has just closed a trap door and is passing Fredesen down the stairway. A cord or cable (possibly an extension cord) is visible fluttering besides Rotwang's right foot.
When Maria is pulling the levers to activate the gong, she acts as if they were hard to move. Yet in several shots the levers are actually loose and move quite freely (especially when Maria or one of the kids bumps them).
Maria is preparing to leave the catacombs and Rotwang has sneaked in to kidnap her. He diverts her attention by throwing a loose brick to the ground a short distance from himself. The candle Maria is holding is probably a prop that is actually a gas burner. A hose or cord (possibly a gas supply hose) is visible on the ground behind her on her left. She turns to her right and walks. The hose is pulled by her right heel.
Fritz Lang shot more than one version of this movie. There are differences between the version on the Madacy DVD and the Kino DVD. In the Kino DVD, Freder exits the Moloch machine hall in chapter 7 (at around 55 mins). The shot of Freder descending the stairs is missing two motorized utility carts. These appear in the Madacy Video DVD in Chapter 3 (at around 24 mins).
On the Kino DVD, a shot in chapter 7 that lasts nine seconds is backwards. The shot starts at 16 minutes, 33 seconds. It is the third of four cityscape shots in a row. The vehicular traffic in this third shot moves on the left side. The traffic moves on the right side in the second and fourth shots. There is a backward script letter "B" on the left side of the third shot. These indicate the third shot is backwards. If the third shot is reversed, it becomes apparent that it is a close-up of the bottom of the fourth shot.
In the Kino Video DVD, the cityscape shot that ends in Chapter 7 (at around 1 min) is cut short. It ends before a dirigible crosses the top of the shot flying from right to left. The dirigible appears in the Madacy Video DVD in Chapter 3 (at around 21 mins).