Continuity mistake: When Gus disconnects the computer Superman lies flat on the floor. A shot later his right shoulder is raised, and his body rests on his left side.
Continuity mistake: Gus serves Brad an extra shot of vodka. He takes a sip and says "yeah, perfect." In the following shot the club in his fist is protruding less than in the previous shot. (00:44:06)
Continuity mistake: The shot outside of the bus where Jimmy and Clark are shows a woman and a man sitting on the front seats. In the shot inside the bus they disappear.
Continuity mistake: When Gus breaks the lattice in pieces and skis away, in the immediate wide angle all the falling wood and debris has disappeared.
Continuity mistake: At the snowy terrace, Gus tells Ross that Superman "is bad." Ross has his index finger pointing at his temple, but a shot later it's lowered. (00:54:53)
Continuity mistake: When Superman struggles to stop being dragged by the computer, there is debris all over the floor. When the computer explodes the debris disappears.
Continuity mistake: When Superman takes Clark's glasses, he folds one arm of the glasses in. A moment later, that arm is extended, and he folds both arms and crushes them.
Continuity mistake: When the toy penguin waddles into the smudge pot, its right wing and head catch fire. When Clark sees it, only a small amount of flame is on top of the head.
Continuity mistake: In the junkyard, when Clark comes out of the container, the hole he produces changes shape depending on the angle.
Continuity mistake: Evil Superman is chasing Clark on a conveyor belt and starts to shout and move swiftly as if he was flying. A frame later, from another angle, he is calmed, walking and repeating all previous movements.
Continuity mistake: When Gus is biting Ross, his hand rests on Gus's cheek, a frame later it rests on his head.
Continuity mistake: When Ross is staying late at work, two women are taking their tennis shoes off. When the angle changes, the woman on the left is walking towards her locker and grabbing her tennis shoes again.
Continuity mistake: Noticeable hand-double during the close-up of Gus unscrewing the fuse: Very dark skin and long fingernails as opposed to Gus's short nails and light-brown coloured hands.
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.
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