Continuity mistake: During the trial, Zod and Ursa swap places in a couple of brief shots.
Continuity mistake: At the end of the football game, a guy with a cap tells Clark to have the clothes ready. But his lips are not in synch.
Continuity mistake: When Clark Kent falls out of the window of the Daily Planet and turns into Superman you can see that he is still wearing slacks and not blue tights.
Revealing mistake: When Otis first arrives in Luthor's lair beneath the train station, he knocks a table lamp over. When the lamp shade comes off the lamp, the bright, exposed light bulb then dims to a less-distracting level for filming purposes. Otis then replaces the shade upon the lamp, and the bulb then instantly goes back to its original level of brightness, so that it will look appropriately illuminated through the shade. The bulb's brightness was manipulated off-screen to conform with the needs of the bulb's effect on the scene.
Continuity mistake: By the cradle, Jor-El and her wife are standing a couple meters apart. In the next shot they appear closer together.
Continuity mistake: While being mugged in the alley, Clark's gabardine keeps swapping between neatly folded to wrinkled between shots.
Continuity mistake: When Lex Luthor calls Superman and the dogs bark, a group of trash cans disappear from the right of the black and white dog.
Continuity mistake: The close shot of the dogs and the garbage bins shows stuff on top of the bins. In the next angle they're gone.
Continuity mistake: When Lois is hanging from the helicopter, she looks down and sees some cars on the pavement, by the entrance of the Daily Planet. From a ground view the cars are gone.
Continuity mistake: The morning Clark leaves the home farm, the sky keeps changing throughout the sequence: Dawning, clouds, sunny, dawn again, cloudy, back to sunny.
Continuity mistake: Superman saves Air Force One lifting the wing with his right hand and then salutes with his right-hand, suddenly holding the wing with his left.
Continuity mistake: When young Clark is left cleaning the football equipment, the students' car drives away, passing by a blue pick-up. The engine noise fades away and silence falls. When the shot changes, the car is suddenly meters behind, next to the blue pick-up, engine roaring again, and leaving the place again.
Continuity mistake: Mr. White dismisses the surrounding people while holding a cigar in his hand. From the opposite angle it's in his mouth. (01:20:26)
Continuity mistake: Superman arrives at Lois' place, arms crossed. Then uncrosses them and lowers his left arm. From the opposite angle it's bent.
Visible crew/equipment: While Lois chats with Clark and says "three kids, two cats" a microphone is reflected on a glass on the lower right corner. (01:03:50)
Continuity mistake: When Teschmacher climbs the bridge she is barefoot, but when she arrives to the truck she is wearing high heels which were nowhere to be seen in her utility belt.
Continuity mistake: When Superman arrives at Lois' place she says "Don't fly away" and her hands are against her chest. A shot later her arms are extended.
Continuity mistake: When Johnathan Kent has a heart attack he passes by a harvest machine, walks several meters and collapses next to the house. In the close-up where he grabs his arm he's moved several meters behind and is next to the machine.
Continuity mistake: When Ms. Teschmacher saves Superman from drowning he is face up, but a shot later he is face down and swimming.
Continuity mistake: After Clark jumps over the railroad track there's a close-up of the train speeding by and it's obviously empty, no sign of the people that were previously seating inside.
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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