If you’ve ever wondered why the performances of terror in the first Alien movie feel so real, here’s your answer: the actors had no idea what the hell was about to happen in Alien’s infamous chestburster scene.

A video produced by Vulture recounts how director Ridley Scott kept Sigourney Weaver, Yaphet Kotto, and other Alien actors in the dark about the fact a baby Xenomorph was going to burst through John Hurt’s chest. Scott’s logic was that the best way to get across a feeling of authentic fear was to freak out the film’s players.

It’s an idea he returned to for Prometheus, where he frightened the crew members with a similar trick that had a creature flying out of a character’s mouth. So, if you’re an actor signing on to a Ridley Scott project, just know you might be screaming your head off in pure terror on any given day. Thanks, Ridley.