Good acting is one thing, but you can't top a genuine reaction to lift a scene. These are the times directors and co-stars kept their actors in the dark about what was going to happen, thereby creating some of the most natural and iconic moments in cinema.
1. Face vom in The Exorcist
The movie's a masterpiece but the entire shoot sounds like an ordeal for the cast in the renegade hands of director William Friedkin. Not only did he routinely and unexpectedly let off guns to keep the cast on edge, and slapped actual priest William O'Malley, who played father Dyer, in the face, but he also pulled a fast one on Jason Miller, who played Father Karras, when it came to the vom.
Sure, he knew there'd be puke, but he hadn't been told it would be in his face. Instead Friedkin led him to believe the pea soup would hit him in the chest. He completed the scene but wasn't best pleased for the rest of the day.
2. Hans Gruber's fall in Die Hard
Alan Rickman had agreed with the stunt guys that he'd drop 25 feet onto an airbag below to create his fatal fall from the Nakatomi building. The agreement was they'd drop him on a count of three.
Only the stunt guys figured they'd get a better reaction if they dropped him on a count of one – hence the expression.
3. Seeing the set of Willy Wonka and the Chocolate Factory
To get performances that were as authentic as possible, the producers kept the sets inside the chocolate factory completely secret and hidden from the child actors who played the lucky golden ticket winners. It meant that the expressions of wonder and surprise from the kids were all genuine.
Indeed, when we see Gene Wilder's Wonka making his grand entrance, hobbling along with a cane before performing a bit of acrobatics, it was the first time the kids had met him.
4. The Alien chest-burster
Probably the most notorious in the 'surprise the cast' genre is John Hurt's infamous death scene where that pesky little alien bursts forth.
Hurt's castmates knew in general terms what was going to happen ("Its head will move and it's going to have teeth"), but director Ridley Scott didn't let them in on any of the disgusting details. "Everyone [in the crew] was wearing raincoats," Sigourney Weaver told Empire. "We should have been a little suspicious. And, oh God, the smell. It was just awful."
5. The night scenes on The Blair Witch Project
For their low-budget, enormously successful and influential horror movie, directors Eduardo Sanchez and Daniel Myrick wanted everything to feel as real as possible. They reportedly wrote a 35-page outline instead of a full script and asked their three lead actors, Heather Donahue, Josh Leonard and Mike Williams, to improvise most of the film around scenarios that they would drip-feed the cast, as well as having them do their own filming.
Then at night time, while they camped in the woods, they'd do their best to scare the crap out of the three. The result is a very scary film with some of the most convincing sleep-deprived fear performances ever.
6. Brad Pitt gets punched in the ear in Fight Club
The movie is called Fight Club, remember. And this is the pivotal scene when Ed Norton's 'narrator' taps into his violent side and has his first scrap with Brad Pitt's Tyler Durden (or does he? Yes, we all know the twist).
So it's not like Pitt wasn't expecting to be punched. However, he was expecting a punch in the shoulder (or possibly chest, depending what you read). Instead Fincher directed Ed at the last minute to go for an unexpected face-punch. Pitt gets popped in the ear but styles it out like a pro, though he does exclaim: "Why the ear?!"
7. The jewellery box snap in Pretty Woman
Okay, 'shock' might be a bit of an exaggeration to describe Julia Roberts' reaction in weird sex-worker romcom Pretty Woman, but the iconic moment where kerb-crawler Richard Gere shuts a jewellery box containing a fancy necklace on Roberts's fingers did elicit surprise.
She wasn't expecting it and gave a very natural laugh. Director Rob Marshall kept it in.