Continuity mistake: The location of the staircase leading up to the supercomputer's control console changes. When they first enter the computer, it is at the back of the computer behind a lot of electrical machinery and circuits. When Ross comes down to try and get the screw out of Gus's mouth, the staircase has moved right next to the entrance of the computer (where Vera gets turned into a robot later on).
Continuity mistake: The firetruck's ladder Jimmy climbs up during the chemical plant fire changes between shots. In the first shot its a white-framed ladder at a pretty shallow angle. The ladder in the second shot changes to a black and orange one which is at a much steeper angle and the rungs are spaced further apart. Also in the second shot he is much closer to the top of the ladder than the first shot, and there is no way he climbed up the ladder that fast.
Continuity mistake: After Gus unscrews the computer, the lights go off and Superman's corner becomes dark. From the opposite angle it's perfectly lit.
Plot hole: Gus could not know that Superman was in Smallville in order to give him the fake Kryptonite.
Continuity mistake: After Clark kills the bad Superman, he has dishevelled hair but after he flies it's now perfectly combed again.
Other mistake: When Superman uses his heat vision against the mirror, the beam should be reflected just like in Superman 2 with Zod.
Factual error: At the start we see a blind man and his guide dog, who runs off after a smaller dog. Guide dogs are specifically trained not to do this before being given to their owner.
Other mistake: As Lorelei is held on the wall, there appears to be a chrome ball attached to the belt she has on to give a reference point, and animation was added to complete the scene.
Revealing mistake: As Evil Superman quips to Clark about wanting to fly, as he struggles Clark's left shoulder goes a little transparent, showing his image was superimposed over the stunt actor.
Continuity mistake: When good Clark is on the trash compactor about to be covered in metal parts, he lays on a blue car hood. Depending on the angle the hood is barely rusty or very rusty.
Continuity mistake: The three baddies arrive at the warehouse, turn on the lights, and watch the supercomputer, standing by two power generators. Cut to a panoramic view of the computer and the lights are out and the baddies gone.
Revealing mistake: When Clark's sneeze launches the bowling ball, the ball casts no shadow, revealing it's a superimposed image.
Continuity mistake: During the tablecloth scene, while Ross listens to Gus, the coffee pot located a meter to the right appears right behind Ross between one frame and another.
Continuity mistake: At the acid storage room, while the chemist says that the temperature can't rise to much you can see the needle on the background way to the right revealing it's hot. But the next shots of the needle show it on the very left first and rising on the second.
Continuity mistake: When the green car crashes, it leaves a lot of rubble in front of it. In the wide shot, the street is clean.
Visible crew/equipment: When Superman arrives at the steel chimney in the chemical plant, wires holding him are visible.
Continuity mistake: The second hole Gus makes with the axe on the laser ball is smaller a second later.
Continuity mistake: Before Superman fixes the Pisa tower, the Italian seller is seen holding a statue by its base. A frame later he holds it by the side.
Continuity mistake: When Clark is waiting for the steel lid to crush him, he raises his arms up. In the next angle they are down and close to his side.
Continuity mistake: When Gus takes the tablecloth off, he walks on top of the fallen stuff to talk about Superman, and then the amount of stuff left behind keeps changing between shots.
Answer: The only reason that Gus was working with Ross, Vera and Lorelei was because he stole money from the company he worked at. To avoid going to prison, Gus was forced to do anything that they wanted. After realizing that his computer was designed to do anything it was ordered to, including killing Superman, Gus removed a small screw which shut down the power momentarily but, after the computer brought itself back online, Gus attempted to destroy it with an axe to save Superman. Superman saw this and realised he was wrong about Gus and after the computer was destroyed decided to help Gus find a job.
That makes sense, thank you! Been bugging me for years.
Jen Hen
You're welcome.