Continuity mistake: Before Vera is transformed into a robot, her face is covered in thin wires. A frame later they're gone.
Continuity mistake: When Gus stays to work extra hours at the office, there are two girls in the background. A paper on the right appears / disappears between shots.
Continuity mistake: Before the phone booths fall, the street swaps from being in shades to really sunny between one frame and another.
Continuity mistake: At the bowling alley, when the kids are about to choose Ricky, the kid on the left keeps changing between a tall kid to a small one with a hat on, back and forth.
Continuity mistake: Gus takes off the fuse off of the computer crying "I did it", then bends his arm towards his chest. A frame later, the arm is extended outside towards Ross.
Continuity mistake: After Gus places the supercomputer blueprints on Mr. Webster's table, they change positions between shots.
Continuity mistake: When Ricky is laying on the wheat field, the tractor's distance to him increases or decreases randomly.
Continuity mistake: Position of skis in Ross's penthouse changes between shots.
Continuity mistake: When Lana is fixing her car, the road is sunny. In the next aerial shot the car casts a huge dark shadow.
Continuity mistake: At the start of the film, the shape of the cake blob on the man's cap changes between shots.
Continuity mistake: When the roller-skater pushes the trolley, the amount of cars in the background changes between shots.
Continuity mistake: During the wheat field scene, Lana wipes her son's bloody bruise with her sweatshirt, but no bloodstains are visible in following shots.
Continuity mistake: At the beginning of the film, Superman exits the photo-booth and a kid points at him. A frame later his arm is down.
Continuity mistake: At the employment office the way papers are arranged on the counter changes from messy to tidy between shots. Also, the blue stamp behind the red one appears and disappears randomly.
Revealing mistake: When the phone booths fall they don't have any cables attached underneath, revealing they're props.
Continuity mistake: Outside the bar, while the people are watching, Superman raises a glass and drinks a shot of whiskey. A frame later, inside the bar, he is already refilling his glass.
Continuity mistake: Superman saves a drowning man in a car on the middle of the street, but when he takes off he's in a children's playground (the DVD extras show the playground scene was deleted).
Other mistake: While on the skiing slope, Gus catches speed and skis away. The problem is he is always on the flat side of the slope, it's impossible to gain speed.
Continuity mistake: In the bowling alley, right before Clark sneezes, the alley on the left has all its bowls standing. Half a second later there are just 5 standing. No sound of them falling was heard in between these two shots.
Continuity mistake: When having a picnic in the wheat field, Clark and Lana's position to the tree and the car nearby changes between shots.
Answer: There were rumors that Hackman was angry with the Salkind Brothers (the producers) for firing director Richard Donner, though Hackman later disputed saying that. His explanation, though he may have been downplaying the real reason, was that he had a number of other movie projects at the time, and he also did not wish to continually play the same villain in an ongoing movie series.
raywest