Hollywood Weapons

In an iconic scene, Chief Brody hangs onto his sinking boat as a giant shark approaches him with a scuba tank lodged in its mouth; constructing a giant shark on a motorized platform to test if a person can hit, and explode, the tank.

In a classic western, Clint Eastwood -- aka Blondie -- saves Eli Wallach from the hangman's noose three separate times by shooting and severing the rope that he hangs from; recreating each scene and testing the reality of those shots.