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We all love moments in films where the plot takes a jaw-dropping turn. But keeping those big movie twists secret before the film comes out is a tough job - and it isn't just the fans who are kept in the dark.

Sometimes actors aren’t aware of a surprising moment or plot development until they’re actually filming it, because the studio is eager to prevent vital story moments leaking to the public before a film is released.

But sometimes the director might want to evoke a real sense of surprise in their actors when whatever it is actually happens on set.

So here are five plot moments where, if the actors look surprised, it’s because they are.

Star Wars: Episode V - The Empire Strikes Back (1980)

Darth Vader
Image caption,
The Force is strong with him.

The fact that (ANCIENT PLOT SPOILER AHEAD!) Darth Vader is Luke Skywalker’s father was one of the biggest surprises of the whole of the Star Wars saga. Writer George Lucas was determined that no-one find out the film’s big reveal beforehand. For the majority of the shoot, no one but director Irvin Kershner and Lucas himself knew the truth.

He even had stars Mark Hamill and David Prowse (who played the body of Darth Vader, with James Earl Jones later providing the voice) read fake lines when they shot the key scene, dubbing the real lines in at the very last moment in post-production.

This resulted in Luke’s shocking parentage being one of the best kept secrets in movie history.

The Goonies (1985)

The Goonies
Image caption,
Goonies never say die!

In Richard Donner’s action-adventure film The Goonies, the biggest and most impressive set is a full-sized replica pirate ship marooned in a vast cavern. One hundred and five feet long and taking two and a half months to build, it was a major undertaking, in the days before CGI made such giant sets mostly unnecessary.

In order to make sure he captured his young cast’s awe-struck faces when they first saw it, Donner kept them away from the soundstage where the giant set was being constructed. When you see their astonished expressions in the movie, it really is them seeing the incredible set for the first time – or the second. In 2019, star Josh Brolin said he was so awestruck by seeing the incredible set for the first time that he swore, leading to Donner having to re-do part of the sequence.

Alien (1979)

Alien
Image caption,
You still don't understand what you're dealing with, do you?

For most viewers the most memorable moment in Ridley Scott’s space-horror flick Alien is the ‘chestburster’ scene, when an alien baby emerges from the stomach of Nostromo crew member Kane (John Hurt).

It’s still a shocking scene, and if the other actors’ reactions seem realistic, it’s because when they filmed the scene Scott had kept exactly what was about to happen a closely guarded secret. He rigged the special effects and then let the cameras run. Recalling the making of the scene to Empire magazine, actor Yaphet Kotto said: “Oh man! It was real, man,”

"We didn't see that coming. We were freaked. The actors were all frightened.”

Casablanca (1942)

Casablanca
Image caption,
Kiss me. Kiss me as if it were the last time.

Set in French Morocco during World War Two, Casablanca stars Humphrey Bogart as Rick Blaine, whose past returns to haunt him when former, now married, lover Ilsa (Ingrid Bergman) walks into his bar.

She and her husband are desperate to escape and need Rick’s help. But during the course of the movie, Rick and Ilsa realise they are still in love . At the end of the film Rick must make an agonising decision: should he ask Ilsa to stay with him, or send her with her husband to safety?

If those unforgettable final moments feel realistic, it's because nobody knew how the film would end right up to the last minute. Scenes were even being written on the day they were filmed.

It might have been stressful for the actors, but many critics wonder if that genuine sense of uncertainty about how this will all turn out doesn’t lend Bogart and Bergman’s performances some of their dramatic power.

The Blair Witch Project (1999)

The Blair Witch Project
Image caption,
It was my fault, because it was my project.

We’ve seen some directors keep parts of the plot secret from their actors, but what about a movie where the cast doesn’t know what’s going to happen at all?

That’s how the writer/directors of cult horror hit The Blair Witch Project ensured that the terror on their cast’s faces was as real as possible.

The actors were sent into the woods with only the briefest notes on their characters. The directors then staged weird events – like making strange noises in the middle of the night, or placing human teeth for the group to find – while the cast, equipped with cameras, filmed their own reactions.

The results were so frighteningly realistic that the film became an instant horror classic.

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