James Cameron’s follow-up to Ridley Scott’s sci-fi masterpiece launched a thousand “Alien vs. Aliens” debates—one of the few times in film history where you could assert that the sequel was better than the original and even be taken seriously. (We decline to take a position on this controversial issue. We love both movies.) Aliens was a giant hit with critics and audiences alike, leading to two more sequels and whatever Prometheus was. In honor of Alien Day, here are some facts about the production to enhance your next viewing of the slimy ’80s action sci-fi classic.

1. CONAN THE DESTROYER HELPED IT GET MADE.

The movie, not the guy. Based on the strength of his script for The Terminator (then in pre-production), James Cameron was approached by 20th Century Fox to write an Alien sequel. But the outline he came up with for Alien II got a lukewarm reaction at Fox, and the idea was put on hold for the time being. Then, as luck would have it, the start date for The Terminator was pushed back nine months so that Arnold Schwarzenegger could make Conan the Destroyer, the sequel to his 1982 hit (in which Conan had been merely a Barbarian). This extra three-quarters of a year gave Cameron time to write three-quarters of a full screenplay for Alien II, not just an outline. (He also co-wrote Rambo: First Blood Part II during this time, by the way.) The Fox bosses liked what they read. Cameron was told that if The Terminator proved successful, he could write and direct the Alien sequel.

2. IT TOOK SEVEN YEARS TO GET THE SEQUEL MADE.

Why did it take seven years to get a sequel made? Lawyers and money, of course. Talk of a sequel began shortly after the original Alien (1979) was a hit, but it was delayed because of a dispute between the film’s producers and 20th Century Fox over the distribution of the original movie’s profits. Fox, reluctant to make a sequel because it would be expensive, finally agreed to it as a way of settling the beef with the producers—basically, “We won’t give you any more of the first movie’s profits, but we’ll greenlight a sequel, and you can make money from that.” (Amusingly, the same producers plus Cameron and Gale Anne Hurd sued Fox again after Aliens, claiming the studio had used “creative accounting” techniques to avoid paying them.)

3. SIGOURNEY WEAVER WAS PAID $35,000 FOR THE FIRST FILM, AND $1 MILLION FOR THE SEQUEL.

James Cameron and Gale Anne Hurd (who became Mrs. James Cameron during pre-production) helped Weaver get what she deserved—first by refusing to make the film without her, and also by refusing to keep it a secret that she was the only person in consideration for the lead role. Fox especially didn’t like that second point, as it put Weaver’s agent in a very strong bargaining position. Sure enough, Weaver got $1 million and a percentage of the profits. It got better for Weaver as the franchise went on, with $4 million for Alien 3 and $11 million for Alien: Resurrection.

4. THERE WAS A LOT OF K-Y JELLY ON THE SET.

All that alien slime and drool? K-Y lubricant. (In case the Freudian sexual nightmare of the creature designs wasn’t strong enough.)

5. THE ACTORS PLAYING SPACE SOLDIERS TRAINED WITH REAL MARINES.

Sigourney Weaver, William Hope, and Paul Reiser didn’t join them because of other commitments, but their characters weren’t supposed to be trained soldiers anyway.

6. THE SET WHERE THE ALIEN NEST IS FOUND SHOWED UP IN TIM BURTON’S BATMAN.

It was a defunct power station, called Acton Lane, and it had the right atmosphere for Aliens. It later appeared as Axis Chemicals, which is where Jack Napier falls into some acid and becomes Joker-fied in 1989's Batman. Parts of the alien hive were still there when Burton and his crew came in, which must have freaked them out a little.

7. THE NOVELIZATION HAS SEVERAL KEY DIFFERENCES.

Alan Dean Foster wrote the paperback versions of the first three Alien films (not to mention some titles in the Star Wars, Star Trek, The Terminator, and Transformers franchises), working from the screenplay before the film was even finished shooting. He stuck closely to what Cameron had written, but there are some major differences. Among them:

- Newt is about 12 years old in the movie, but six in the book.

- Ripley becomes more despondent after the tribunal, withdrawn and depressed, living in a filthy apartment and clearly traumatized by her past. In the movie, of course, she’s a lot tougher.

- Ripley immediately realizes Bishop is an android (though she still doesn’t confront him until later). Also the scene with Bishop’s famous knife trick isn’t in the book.

- There are several colonists still alive on the alien planet, not just one woman.

- Ripley opens fire on the Queen as soon as she sees her, rather than “negotiating.”

- When she is cornered by the Queen, Ripley intends to throw herself and Newt over the railing to die rather than fall into the Queen’s clutches.

8. PART OF THE REASON ALIENS IS SO GOOD IS THAT JAMES CAMERON USED THE TERMINATOR AS PRACTICE.

“I was thinking of Terminator as a movie no one would see, so I could work on some of the things that I would use on Aliens,” Cameron told the Los Angeles Times. “I remember when I was shooting a scene where [the heroine] crawls through all this machinery, I thought, ‘This will make a good dry run ... I’ll get some of this stuff worked out so I’ll know how to do it.'"

9. IT’S THE ONLY ACTING THAT CARRIE HENN, WHO PLAYED YOUNG NEWT, EVER DID.

Henn was nine years old and living with her family at a U.S. Air Force base in England when casting agents found her. She loved the experience, remained friends with Sigourney Weaver afterward, was invited to the premiere of Alien 3 (even though she wasn’t in the movie) ... and never acted again. Instead, she became a schoolteacher.

10. THE CREEPY DERELICT SHIP WAS THE SAME ONE USED IN THE FIRST ALIEN.

Fox hadn’t immediately planned on making a sequel, so they didn’t keep the sets and models lying around. Luckily, a collector named Bob Burns had the original model (and numerous other Alien artifacts) preserved at his home.

11. CAMERON HAD TO QUASH A MUTINY ON THE SET.

The film was shot at England’s historic Pinewood Studios, which provided its own unionized crew members for productions using the facilities. Some of these workers resented the 14-hour days and, having no idea what Cameron was capable of (The Terminator hadn’t opened yet), thought he was in over his head. In particular, the first assistant director thought he should be directing Aliens. He mocked Cameron, called him “guv’nor,” rolled his eyes at him ... and got himself fired for insubordination. The new first assistant director behaved respectfully, and things were better after that.

12. SIGOURNEY WEAVER DIDN’T WANT TO USE A GUN.

She’s not a fan of them, and she lobbied Cameron to let Ripley go the entire film without using one. Cameron talked her into it after taking her to a shooting range and showing her how fun it could be. (“Another liberal bites the dust,” he joked on the DVD commentary.)

13. GALE ANNE HURD’S HANDS MAKE A CAMEO IN THE FILM.

Jenette Goldstein, the actress who played Vasquez, didn’t have any firearms training. She couldn’t hold a gun properly, which was noticeable when seen in close-ups, so producer Gale Anne Hurd served as her hand double.

14. JAMES HORNER HAD THREE WEEKS TO WRITE THE SCORE.

James Horner thought he’d have six weeks to write the musical score. Instead, he had three weeks, and had to write some parts overnight. The movie was behind schedule, not even finished being filmed (let alone edited) when Horner arrived in England. What’s more, the recording studio he’d been provided with was outmoded, not equipped to handle the synthesizers he wanted to use. Horner called the experience a “nightmare,” and ended up writing the climactic musical cue overnight. Coming away with the impression that a James Cameron film was too stressful and rushed, he figured he’d never work with the director again. And he didn’t ... until Cameron approached him for Titanic. (That rushed Aliens score earned Horner an Oscar nomination, by the way.)

Additional Sources: Commentaries and featurettes on the Aliens Blu-ray.