Continuity mistake: The rock that hits the prop-astronaut blows his head off. Seconds later the head is back in place.
Factual error: When Superman addresses the UN, the delegate presumably representing the United Kingdom appears behind an "England" sign - "England" is not an international entity represented at the UN, while the United Kingdom of Great Britain and Northern Ireland is. (00:32:20)
Audio problem: On the moon, Superman smashes Nuclear Man's head against his knee. The clonk is heard before the hit (even forgetting that sound can't be heard on the moon).
Continuity mistake: Lois visits Clark and takes her coat off, folds it and places it on her arm. A frame later the coat is lying on the couch.
Continuity mistake: When Clark is about to enter the subway train, the people by the door appear and disappear all the time: A cop, a man with a hat, a lady in a leather jacket.
Revealing mistake: When Superman flies towards the volcano, the scene of the eruption he is superimposed on is exactly the same one we saw 2 minutes earlier.
Continuity mistake: When Superman throws Nuclear Man down the chimney, the sky is grey and cloudy, but a second later it's pitch black.
Plot hole: Nuclear Man makes his appearance at Lex's house, walks a couple meters and faints "because of lack of sun" according to Lex. This makes no sense, the place is surrounded by windows and there are beams of light everywhere. There are many scenes where he moves around in rooms with the same or less light without suffering the least damage. In this specific scene he simply faints because it's good for the plot.
Continuity mistake: Lois visits Clark at his appartment and a wooden duck, with the head painted green and white and a black coloured body, appears on the table next to her.
Continuity mistake: Outside the UN, the crowd looks up to the sky and watch Superman come flying. When he lands, 2 seconds later, all the stunts on the first row are either gone or standing somewhere else. A kid on the right with dyed hair, for example, is now standing way behind the crowd.
Continuity mistake: On the Great Wall, a woman with a turquoise jacket stumbles and is about to fall off the edge. From a new angle two seconds later, she is three meters behind and stumbling towards the edge again.
Continuity mistake: After the volcano erupts, the boy standing to the right of the girl disappears between shots.
Other mistake: In the rest of Superman movies, whenever he used his eyes to do some trick a beam came out. In this (really cheap) movie the beam is gone.
Revealing mistake: When Superman drops the elevator containing the imprisoned Nuclear Man on the moon, he flies off and lands to straighten the American flag. In this shot you can plainly see the wires helping him land.
Continuity mistake: During the Great Wall of China scene, the sky changes from cloudy and grey in the shots involving people, to bright and sunny when the wall explodes.
Continuity mistake: When Lacy is about to enter the elevator, a light brown rug has appeared on the floor behind, which disappears in the next wide shots.
Continuity mistake: In the museum, while the guide is walking towards Superman's hair, people suddenly appear on the left taking pictures.
Continuity mistake: When Superman arrives at the UN, Jimmy Olsen stops in the middle of the street to take a picture of him. A shot later he's six feet behind a dark car.
Plot hole: The SWAT van could have never gotten where Nuclear Man is because of the humongous traffic jam.
Revealing mistake: After they fall off the balcony, Superman chases Nuclear Man, but the boats beneath don't move.
Answer: Lacy had gotten tired of her dad's newspaper, big-city life and decided to move to Smallville because she wanted to experience life at a much slower pace and even decided to live on a farm.