The Spanish version of the title translates as "Alien: The 8th Passenger. "
Originally to be directed by Walter Hill, but he pulled out and gave the job to Ridley Scott.
Roger Dicken, who designed and operated the "face hugger" and the "chest burster," had originally wanted the latter to pull itself out of Kane's torso with its own little hands, a sequence he felt would have produced a much more horrifying effect than the gratuitous blood and guts in the release print.
The alien's habit of laying eggs in the stomach (which then burst out) is similar to the life-cycle of the tsetse fly.
A lawsuit by A.E. van Vogt, claiming plagiarism of his 1939 story "Discord in Scarlet" (which he had also incorporated in the 1950 novel "Voyage of the Space Beagle"), was settled out of court.
Much of the dialogue was ad-libbed.
An early draft of the script had a male Ripley.
Veronica Cartwright was originally to play Ripley, but producers opted for Sigourney Weaver.
In the scene where Dallas, Kane and Lambert are leaving the ship, the actual actors walking past the Nostromo's landing struts are 3 children (two of whom were Scott's children dressed in scaled down spacesuits.
This has the effect of making the ship look bigger.
A sex scene between Dallas and Ripley was in the script, but was not filmed.
The front (face) part of the alien costume's head is made from a real human skull.
The rumor that only John Hurt and the crew knew exactly what was going to happen during the stomach-bursting scene is false.
"Nostromo" is the title of a Joseph Conrad book.
The shuttle that Ripley escapes on is called the "Narcissus", a reference to another Conrad book.
See also Aliens (1986).
Conceptual artist H.R. Giger's designs were changed several times, because of their blatant sexuality: the top of the eggs resembled a vagina too closely.
Extra scenes filmed but not included, due to pacing problems:
Ripley finds Dallas and Brett cocooned.
Dallas is covered in maggots and begs Ripley to kill him. She does so with a flame thrower.
Ripley and Lambert discuss whether Ash has sex or not.
Alternative death scene for Brett: Ripley and Parker come across an alive Brett being lifted from the ground.
Scott is reportedly quoted as saying that originally he wanted a much darker ending.
He planned on having the alien bite off Ripley's head in the escape shuttle, sit in her chair, and then start speaking with her voice in a message to Earth.
Apparently, 20th Century Fox wasn't too pleased with such a dark ending.
The Polish title, translated back to English, is "The 8th passenger of the Nostromo."
Continuity: In the opening scene, when we see the reflection of computer screen on the helmet, camera shows the computer screen and we can see a cup on the right of the screen.
When camera shows the helmet second time and then the screen again, the cup is gone.
Continuity: Each astronaut wears a leather flying helmet under their space helmet.
Yet when Kane's helmet is cut off to reveal the face hugger, his leather helmet has vanished.
Continuity: Brett's cigarette when Ripley confronts him about the way he responds to questions.
Continuity: Whether Kane's shirt is tucked in or not during his death scene.
Continuity: The alien's tail snakes between Lambert's feet, but it's not her feet that are shown.
Lambert wears cowboy boots; Kane wears joggers.
Continuity: Mother's two 30 second countdowns take 36 and 37 seconds respectively.
Revealing mistakes: During Parker's fight with Ash, the sleeve on his right shoulder suddenly becomes torn and a safety pin is visible holding it together.
In the next shot we see his shirt intact and we see Ash tearing it.
Factual errors: The alien skin incorporates silicon for reinforcement.
What food source could have allowed the alien to grow to about human size (and perform other metabolic functions) while supplying enough silicon?