4. The Cast Didn't See The Crawlers Until Their Debut Shot - The Descent (2005)
The Descent is a movie about a group of female explorers who go underground to navigate a cave system and find themselves facing off against an ancient race of monsters. These monsters, known as "Crawlers," are evolved and adapted perfectly to their dark, hostile environment, and are - plainly put - absolutely terrifying. According to director of the movie, Neil Marshall, he purposely avoided showing the all-female cast what the Crawlers looked like until the big reveal, which he planned to film in one take to gauge their honest reactions. One the shot was set up, the actors were told to react as they thought appropriate (they still weren't sure what it was they were going to see), but to
stay in the same place. This did not go as planned. Upon sighting the first Crawler, the cast were so frightened by what they were suddenly found themselves looking at, that they rushed out of frame and cowered in a huddle on the other side of the set. According to the production team, it wasn't all bad, though - they carried the same fear factor through to the next take (one where they all managed to stay put).