Remember the chest-burster? If you've seen Alien, you will: a great maw of viscera that appears to shoot through John Hurt's body as it lies on a table, with blood and guts pumping in every direction.
Veronica Cartwright probably remembers little else. Cartwright was initially dubious about accepting her part in Alien as the ship's navigator Lambert, because she didn't like the character's ''emotional weakness''. When that stream of blood hit her, however, she was so shocked she fell over, screaming with genuine distress. Awesome!
Prometheus - Trailer
A team of explorers discover a clue to the origins of mankind on Earth, leading them on a journey to the darkest corners of the universe.
But that's what Ridley Scott did with Alien, way back in 1979: launched the slasher genre, along with reworking Hitchcockian suspense, rewriting horror and, most importantly for fans everywhere, changing the way science fiction could and henceforth would be done. Because, hard as it is to remember now since it became the gold standard, Alien wasn't like other sci-fi. What was particular about it - and what made genre-resistant critics pay homage - was its atmosphere of dread. Andrew O'Hehir in Salon, for example, saw it as ''a film about human loneliness amid the emptiness and amorality of creation''. And, on another front altogether, it set up a new kind of action heroine in Ellen Ripley, played by the then-unknown stage actress Sigourney Weaver.
Alien's success was such that it led to three sequels, all featuring Ripley, and two crossover films with the Predator franchise, several illegal spin-offs and a host of games and comics. The last of the sequels, however - Alien Resurrection (1997), directed by the unlikely choice of Jean-Pierre Jeunet - was seen as bad enough to have snuffed out the franchise. Except that now, as every fan knows, Ridley Scott has returned to Alien territory 33 years on with a kind of prequel - Prometheus.
The starting point for Prometheus, Scott says, was the moment in Alien when the Nostromo crew finds a deserted spaceship with a corpse in the pilot seat that became known to fans as the space jockey. The space jockey's story was never told but became one of the little knots in the fabric of the story endlessly unpicked by fans and, now, by Scott himself. ''It's interesting when you start with an idea like that,'' he says. ''You don't know if it's going to be a prequel or a sequel, but it gradually adjusted itself into much larger questions and now the connection to the original Alien is barely in its DNA.''
Secrecy surrounding the project was such that before the final scriptwriter, Damon Lindelof, was on board, he was given two hours to read an earlier draft while a guard waited outside the door.
Given this level of security, a press conference to discuss the film is more tantalising than informative; journalists are not even allowed to record it. Clips and trailers drip-fed through the internet, however, have already revealed that many of the original themes have been preserved. As in Alien, the space vessel Prometheus' voyage is being funded by a vast and omnipotent corporation, which has its own agenda and a corporate commander on board, in this instance Charlize Theron at her most queenly. There is, once again, a disturbingly human android, played here by Michael Fassbender. Scott hasn't got Ripley - as far as we know, anyway - but he does have the prime kick-arse gal-of-the-moment, Noomi Rapace, lately of the Swedish version of Girl with the Dragon Tattoo, to play a venturesome archaeologist.
Rapace's Elizabeth Shaw is the daughter of a priest, wrestling with reconciling scientific rationalism with a belief in God.
''She has the great gift of believing,'' Rapace says. ''It's an interesting conflict we talked about a lot. She is a true believer but then things happen and she becomes a survivor, a fighter and a warrior in a way. I'm not sure she is so convinced by the end of the movie.''
Fassbender talks about watching Dirk Bogarde in The Servant to study subservient body language; Theron about doing push-ups. There is not much they can say, but then it's really Scott who is the star here, as much a brand in his own right as the Alien franchise.
Scott began his career as a designer, which is crucial in science fiction generally and to the ambience of the Alien films in particular. In the original film, designs for the monster and other biomechanical devices were the work of Swiss surrealist artist H.R. Giger, using Freudian motifs suggesting genitals. Ron Cobb designed the ship, much of which was assembled from scrap. Three decades later, many design ideas that were then revolutionary are exhausted. ''One of the problems with science fiction, which is probably one of the reasons I haven't done one for many, many years, is the fact that everything is used up,'' Scott says. ''Every type of spacesuit is used up, every type of spacecraft is vaguely familiar, the corridors are similar and the planets are similar. So what you try to do is lean more heavily on the story and on the characters.'' At the same time, he says, ''I think we came up with a lot of fairly cool-looking things.''
And then, of course, there was 3D, which Scott says is much easier to handle than the modern shamans of techno-geekery would like you to think. ''It's not science; it's not brain surgery,'' he says. ''Because I'm a visual person anyway, it was dead simple and very straightforward.
''You could easily allow things to turn into major conferences where you ask anyone, including the tea lady, what she thinks, but I don't do that. If you know what you want, you know what you want. You can have a 45-minute discussion about something hanging in the foreground. Say 'I hate it, get rid of it' or 'I love it, f--- off!' It's that simple!''
In one of the online Prometheus clips, Guy Pearce as corporate mogul gives a potted history of technological endeavour, from Prometheus' theft of fire from the gods to the new decade of biotechnology. ''We are the gods now!'' he says portentously.
In genre movies, people claiming to be gods always invite the worst to happen; hubris is always punished. But in the creation of movie sci-fi worlds, Sir Ridley Scott is definitely a god. He stole the fire when he made Alien. We now look forward to seeing him make it burn.
Prometheus opens on June 7.