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 wide shots where we see Kane and Co. walking around outside the Nostromo, Ridley Scott used children (two of which were his own) in special child sized space suits so the sets would appear bigger in comparison to the people on screen. He used the same tactic again when they discover the fossilised space jockey on the alien ship.
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: It's another race of space alien that is also subject to infection by the Aliens. This particular one was infected and moved as far as it could from its race's known space and broadcast a warning before it died. The presence of eggs in the hold may indicate that it was a research ship. The race was never used in other Alien movies because it adds a new dynamic to the plotlines: two alien species, locked in mortal combat and neither particularly friendly with humans. In the Alien pseudo-prequel Prometheus we learn these beings are known as the Engineers and have interesting ties with both the aliens and humans as well.
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