Trivia: Ripley abruptly yelling at Parker to "Shut up!" is not in the script. Fans and industry gossip have long speculated that this was Sigourney Weaver breaking character in frustration and she was in fact telling Yaphet Kotto to "shut up" so she can finish her lines. The sequels 'Aliens' and 'Alien 3' both feature scenes where one of the normally cooler-headed protagonists suddenly snaps at a ranting character to "shut up!" in apparent reference to this moment. (01:16:50)
Trivia: The clear slime that the alien dribbles is actually KY jelly.
Trivia: During the opening sequence, as the camera moves through the corridors of the Nostromo, a Krups coffee grinder can be seen mounted to one of the walls. It happens to be the same model as the "Mr. Fusion" in Back to the Future.
Trivia: Harrison Ford turned down the role of Captain Dallas.
Trivia: After first seeing the film, Stanley Kubrick called up Ridley Scott to ask how they did the chestburster scene. Scott not being used to fame at the time and Kubrick being one of his career idols, Scott assumed he was speaking with an imposter playing a prank, and promptly told Kubrick to "fuck off."
Trivia: Despite (or maybe because of) their similar style, a bitter rivalry developed between artists H.R. Giger and Roger Dicken. Giger said Dicken's work looked "terrible, like a dinosaur from Disneyland." Dicken in turn called Giger's designs "repulsive abominations." In response, Giger described Dicken as "an awfully aggressive nut" who was "on the verge of a nervous breakdown." The finished film features both artists' designs: Giger's adult xenomorph, and Dicken's facehugger and chestburster.
Trivia: The tendons in the creature's jaws were made using shredded condoms.
Trivia: Writer Dan O'Bannon's idea for Alien evolved from a comedy B movie he'd written a few years earlier called Dark Star which featured an alien that was a beach ball. O'Bannon said that he was unhappy with the silly alien in "Dark Star" and deliberately steered away from potentially comic elements while writing "Alien."
Trivia: For the landing sequence the crew rigged paint mixers beneath the seats on the bridge set so that they would vibrate to simulate turbulence. One effects supervisor noted wryly that when they turned them on Sigourney Weaver would get "a little smile on her face."
Trivia: As well as being allergic to glycerine, Sigourney Weaver was allergic to Jones. She didn't know that she was allergic to cats and thought that Ridley Scott might have her replaced, however he didn't mind as long as she didn't.
Trivia: A few scenes that showcased the crew's casual attitude toward sex and bisexuality were planned at various points, including: a sex scene between Ripley and Dallas after Kane's death; a "post-coital" moment between Dallas and Parker; and a moment in which Ripley speaks intimately with Lambert and finds it odd that Ash hasn't tried to sleep with either of them. This last scene was the only one of these filmed and it, too, was cut in order to make the crew relationships more ambiguous.
Answer: According to the commentary on the DVD, Ridley didn't add this scene to the original cinematic release because he thought it revealed the true horror of the Alien too soon in the film. The scene is quite early in the film and he thought revealing the fully matured Alien at that time would reduce the viewer's fear.
I had watched Alien several times before I noticed the Alien hanging there.At this point the Audience have no idea what the Alien looks like, they're looking at pieces of science fiction equipment put in by the production crew that they can't relate to, so for all they know the Alien could just be a piece of kit hanging there.