That Alien chest-burster scene? The actors didn't see it coming.

As surprised as you might have been the first time you saw the creature burst out of John Hurt's chest in Alien, the actors were even more shocked. That's because they didn't know it was going to happen.

In Dan O'Bannon and Walter Hill's script, the description merely read, "the thing emerges." Hoping to elicit authentic responses from the actors in the scene, Ridley Scott engineered the practical effect in private. "If an actor is just acting terrified, you can't get the genuine look of raw, animal fear," he told Empire Magazine.

"In those days prosthetics weren't that good," Scott continued. "I figured the best thing to do was to get stuff from a butcher's shop and a fishmonger." That's right: the blood and guts are cow organs, clams, and oysters. "You can't make better stuff than that," said Scott. "It's organic."

On the day of the scene, Scott had his team stuff Hurt's "chest cavity" with the baby Xenomorph and butcher's organs. They pumped stage blood into a couple of hoses and, when the moment was right, set the gag in motion. Actress Veronica Cartwright was immediately hit by a spurt of blood; she was so shocked that she passed out on the spot.

As if scaring his actors half to death just once wasn't enough, Scott surprised crew members with a similar trick on the set of Prometheus when he rigged a creature to fly out of a character's mouth.

A new video from Vulture details the "gut-wrenching" process from Alien: