Although Denzel was using an empty gun with a solid filled-in barrel, the recoil was enough to make Idris believe he'd really been shot.
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"[Frank] goes down the street and Idris Elba is standing there saying, 'Hey, what are you going to do, shoot me, Frank? Go on, shoot me Frank in front of all these people.' And he just goes boom and shoots him on the spot," director Ridley Scott told The Daily Mail of the scene.
Ridley explained that before filming he had asked Idris to lean his head into the empty gun in order to add realism — but Idris didn't know the recoil would truly shock him.
"What happened was I said to Idris, 'Listen, when he puts the gun to your head, lean on the gun.' Because, by the way, this is a gun with a solid barrel; there is no aperture. I would never risk it. But when you pull the trigger there's a recoil. There's no blank, nothing. So I said, 'I want you to lean on the gun,'" Ridley explained.
He continued, "He pulled the trigger and it goes bang. Idris thought he'd been shot and dropped to the sidewalk and said, 'I've been shot!'"
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While Idris must have had a scary few moments, firearms expert Paul Biddiss, who works with Ridley, reiterated that the actor was never in danger and explained how it worked.
"He is very hot on safety. What he was referring to by a solid barrel is a completely filled in barrel that no bullet would be able to pass through, so it was a completely deactivated impractical gun as far as firing anything was concerned," Paul shared.
He added, "He was still able to create a recoil effect for the film's purposes by using something used in films called a UTM round which can be put in a weapon that has had the barrel completely filled, and it still causes a blowback. It is like a small silver case with compressed air that reacts. It can be used repeatedly for a recoil effect each time."
