Continuity mistake: When baby Clark is greeting the Kents inside the cocoon, Martha's hands change from resting on the sides to up.
Continuity mistake: In the footbal field, one of the megaphones that Clark kicks down appears on the bench in the following shot.
Continuity mistake: The position of the baby when his mother holds him by the cradle differs in the wide and close shots.
Continuity mistake: When the truck falls on Jonathan Kent, the way Martha holds him changes between shots.
Continuity mistake: When the player takes Susie with him, a bucket appears from nowhere on the right side of the bench.
Continuity mistake: After Clark runs by the train, a girl in a moving car stands up. In the next angle, a split second later, she is sitting down.
Continuity mistake: When the football game ends, Clark is holding a bundle of towels. A frame later, the towel is neatly folded.
Continuity mistake: Before Superman enters Luthor's lair, Teschmacher is laying on the couch and a bottle of Ambre Solaire is facing straight close to the TV. In the next shot the bottle is turned to the left.
Continuity mistake: After Lex Luthor opens the box with Kryptonite, Superman leans with both arms on a table. A second later he's leaning with just one arm.
Continuity mistake: The first day Clark Kent works in the Daily Planet, he sits by his desk and then a close-up shows Lois placing her hair behind her ear. In the next shot the hair has changed and is now is covering her ear.
Continuity mistake: The day young Clark Kent leaves his parents' home, there's a shot where mother is watching him from inside the house. The clouds and sky colour reflected on the glass is different to the one we see in the following angle.
Continuity mistake: After Jor-El places the green crystal on Khal-El pod, it keeps changing place.
Continuity mistake: Near the end of the movie when Superman pulls Lois Lane out of the car and she's already dead, she is very dirty all over because of all the dirt that "drowned" her. In the following shot when Superman is done crying over her and leaves her on the ground to reverse time so that she will come to life again, her clothes are all white and shiny.
Continuity mistake: When the lady of Lex Luthor is in a red dress pretending to be unconscious on the road we see her legs flat on the ground, then in the next shot one leg is standing up.
Answer: He wanted to see for himself if the stories were true. Some reporters tend to exaggerate the facts and if he had any other weaknesses. He couldn't be sure the kryptonite would work.
While I don't exactly disagree that Lex wanted to see for himself how invincible Superman is, I don't think that's the main reason why he did it. The bullets and fire were simply a charade to make it look like this was his security system. Keep in mind, he wanted Superman to enter his lair because the real trap was the Kryptonite that he had in the lead box.
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