Trivia: Jeff East, who plays teenage Clark Kent, was dubbed over with Christopher Reeves' voice. The only time Jeff's actual voice is heard is when he shouts in excitement after jumping past the speeding train.
Trivia: To get the muscular build required to play Superman Christopher Reeve went on a training regime supervised by David Prowse who played Darth Vader in the first Star Wars trilogy.
Trivia: The famous (or infamous) New York City blackout of 1977 occurred during location shooting for "Superman." According to director Richard Donner, cinematographer Geoffrey Unsworth mistakenly believed he had caused the blackout by plugging in a spotlight to a lamppost while filming.
Trivia: When discussing his grand plans, Lex Luthor makes a throw-away line and names a country to be blown up apparently at random. Not quite so random - it was changed in each country of release.
Trivia: Not really a mistake, but I found it interesting that when Clark Kent turns into Superman he takes the time to comb his hair to the other side.
Trivia: If you look very closely when Superman is floating in Lex Luther's swimming pool, you'll notice a small floatation device placed under his cape to keep his head above the water. That's because Superman boots weighed a whole lot after they became filled with water. The floatation device made it easier for Clark Kent to swim during that scene.
Trivia: The voice of the air traffic controller who is talking to the helicopter pilot was done by Christopher Reeve.
Trivia: Something for Cheers fans: John Ratzenberger (Cliff) is an extra, playing a control booth worker.
Trivia: Gene Hackman refused to shave his head - it had to be done by a stunt double.
Trivia: Goldfinger director Guy Hamilton was originally going the direct this film, which was to be shot in Italy. A combination of financial issues and a warrant being issued for Marlon Brando's arrest due to his role in the highly controversial Last Tango in Paris lead to production relocating to England. Hamilton had become a tax exile from the country and was forced to drop out of Superman.
Trivia: Christopher Reeve was initially turned down for the role of Superman because he was too thin. He put on 42 lbs after being cast.
Trivia: Marlon Brando got the highest payment of all the actors in spite of his short time onscreen.
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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