1. The director of Eternal Sunshine of the Spotless Mind would privately tell cast members to do things that the others weren't expecting. In some scenes, Kate was encouraged to play up the comedy, while Jim had been told to be serious.
2. ET was filmed in chronological order and none of the kids had seen the puppet before filming, so their first impressions were totally real.
3. The makers of IT had a similar idea – the kids were kept away from Bill Skarsgård as much as possible so their terrified first reactions could be caught on film.
4. Everyone on Titanic knew that the water was gonna be cold, but they weren't prepared for just how freezing it was. The water was so icy that Kate Winslet couldn't stop shaking during the axe scene.
5. In The Office, Oscar Nuñez had no idea that Steve Carrell was going to kiss him on the lips, and the rest of the cast's shock was completely real.
6. In Mockingjay Part 1, the director filmed and edited test footage of Peeta’s interviews to be played during Jennifer Lawrence’s scenes. Jen was missing working with Josh Hutcherson so he knew showing him on-screen during her scene would provoke an emotional response.
7. The actors hired for the Blair Witch Project were given a 35-page script and were told to improvise. They were taken into the woods, and as you can imagine, the results were terrifying.
8. To recreate the revolutionary spirit, the cast of Les Miserables were told to build a barricade in 10 minutes. The cameras were rolling and what they made ended up being used in the final film.
9. In the episode of Glee where Santana thought Finn was the one who outed her, the director had privately instructed Naya Rivera give Cory Monteith a real full-forced slap.
10. In Willy Wonka and the Chocolate Factory, no one was warned about the boat scene, the creepy tunnel, or Gene Wilder's song, so the children's alarmed faces make a lot of sense.
11. To prepare for Saving Private Ryan, all the main cast members were sent to a harsh 10-day boot camp, except for Matt Damon, who stayed in America. Matt's character was resented by everyone, and he was purposefully excluded so that the on-screen hostility would be as realistic as possible.
12. When Alan Rickman was filming the end of Die Hard, the director told him he’d count him down from three, and let Hans fall to his death after one, but told the stunt team to let him drop on one.
13. During the filming of The Exorcist, director William Friedkin fired a gun on set as a way to get authentic scared reactions from some of the actors
14. Jay Baruchel was so terrified of rollercoasters that he made a deal with Knocked Up director Judd Apatow – he would appear naked in the earthquake scene as long as he didn't have to get on any of the rides. If you've seen the film, you'll know that Judd went back on the deal.
15. Steven Spielberg hired a stunt actor to play the first victim in Jaws. She was attached to a harness and there was a diver ready to pull her underwater. After the first few takes weren't cutting it, he decided to have her pulled under the water when she wasn't expecting it – the shark wasn't real, but her spluttering was.
16. And finally, this one is more a case of actors being kept in the dark than being caught off guard, but still. Four out of the six main cast members weren't told about the huge twist at the end of the first season of The Good Place.
