Fans of the iconic sci-fi horror film Alien have unearthed an unnerving truth about one of its most famous scenes. Director Ridley Scott’s epic feature is a cinematic classic, with fans still keen to share behind the scenes knowledge and production tidbits to this day.

Released in 1979, it tells the story of a crew aboard a spaceship, Nostromo, returning home from a mission. They’re in a form of suspended animation but are awakened when their ship detects signs of intelligent life.

The crew then goes on to investigate, venturing to a derelict alien craft only to find themselves being hunted by a terrifying extraterrestrial that breeds with human hosts. Crew member Kane, played by John Hurt, is attacked by a spider-like creature, which attaches itself to his face.

When he’s returned to his own ship, his colleagues work to remove the creature without harming him. Eventually, the critter detaches from Kane’s face and dies.

Kane wakes up and initially appears to be well, despite the terrifying ordeal. This doesn’t prove to be the case, though.

In a particularly famous scene, the crew are enjoying a last meal before they return to suspended animation when an alien bursts through Kane’s chest, killing him, and escaping into the ship, much to the horror of the remaining crew members.

It is this scene in particular which was discussed in a Reddit thread which asked for films with “significant unplanned, unscripted, accidental, or improvised elements”.

One person shared: “I read somewhere that in the original Alien movie, the scene where the Xenomorph bursts out of the guys chest was only known by the director and select others.

“The script had something very vague, so when it bursts out of his chest and blood goes everywhere, it took all of the actors in that scene completely by surprise and the look of terror on their faces is completely real.”

In an interview shared by the Guardian in 2009, the reality of the scene was discussed at length. Executive producer and screenwriter Ron Shusett revealed: “Ridley didn’t tell the cast. He said, ‘They’re just going to see it’.”

Sigourney Weaver, who played beloved warrant officer Ripley, added: “They were crafty. They pitched the story so that you feel John Hurt's character would be the only true hero among us.” She added: “All it said in the script was, ‘This thing emerges’.”

Director Ridley Scott said: “The reactions were going to be the most difficult thing. If an actor is just acting terrified, you can't get the genuine look of raw, animal fear.”

The clandestine filming method, and keeping the majority of the actors in the dark about what was to happen, proved so effective that Veronica Cartwright, who played ship navigator Lambert, “passed out”.

On Reddit, one Alien fan observed: “You can hear Veronica Cartwright make a very real almost-vomit sound in that scene. It's great.”

The film presented a career-defining role for Sigourney Weaver, who played beloved warrant officer Ripley. Prior to the film, she’d largely been known for her presence on Broadway but impressed Ridley Scott and producers with her audition.

In 2002, Alien was inducted into the Library of Congress and branded “culturally, historically, or aesthetically significant”. It has also been selected for preservation in the United States National Film Registry.