In the theatrical version of Superman II, Lois (Margot Kidder) discovers that Clark Kent (Christopher Reeve) is Superman after he trips over a rug, falls into a fire, and she inspects his uninjured hand. Superman's reveal to Lois played out quite differently in the original script. Lois is convinced that Clark is Superman by this point in the movie. To prove this, she decides to shoot Clark with a revolver. Superman is impervious to bullets, so he's unaffected by the shot and is therefore forced to reveal his true identity. The unmasked Superman remarks that, if she'd been wrong, then Clark Kent would be death. Lois smirks and replies that she used blanks in the gun.
It's a nice scene that reveals Lois's cleverness. Unfortunately, director Richard Donner never got a chance to shoot the scene before the movie's producers fired him, but what we do have are filmed rehearsals between Reeve and Kidder, which is what Donner used for his cut of Superman II in 2006. The footage is obviously not meant for prime time. You can readily tell that Donner shot them separately—and some time apart, considering that Reeve's hairstyle changes between shots. Nevertheless, it's nice that we have some version of this scene, which, even in its unfinished form, is arguably better than the more slapstick version we got in the theatrical cut.