Plot hole: When Ripley goes to access the computer Mother, the entry door opens and closes with a hissing noise, a couple of minutes later you see Ash next to Ripley with a smile on his face. How did Ash manage to open the same door without it making the hissing sound? Ash could not have been in the room before Ripley came in - once Ripley has sat down at the console, it rotates on a 90 degree angle, this would have made it impossible for Ash to be hiding behind a desk or a computer console without being seen by Ripley. There are many doors on the ship that make the same hissing sound when the doors open, an obvious example is the infirmary door. And Ash couldn't have disabled the pneumatics of the door, because when Ripley exits the room, the hissing noise is heard again. (01:18:40 - 01:20:00)
Suggested correction: There's no evidence that sound happens every time the door opens. It may be a pressure release sound, but not enough pressure has built up since Ripley opened the door to make the sound. It's like flushing a toilet twice in quick succession, before the tank has had a chance to refill. The action is the same, but the same mechanism is engaged; it makes a different sound.
Plot hole: The shuttle "won't take four" crew members. Considering it only has two cryotubes (and hypersleep appears to be necessary for any hope of survival), it doesn't seem to accommodate three people, either. (Admittedly I would still go for it, too, if I were up against a 7-foot-tall acid-blooded alien monster with two sets of jaws, but there doesn't seem to be much difference whether there's three or four people onboard).
Suggested correction: As was standard, the Narcissus (which was the name of the shuttle) was designed to carry a crew of three, although the interior could be easily modified to seat more crew members if necessary. For long-duration travel, the shuttle contained two stasis capsules, although long-range interstellar transit was not the vessel's primary purpose. So in a life-or-death situation, four people intending to use it to get off the Nostromo isn't a plot hole.
I'm not sure I understand the correction. The reason Ripley rules out escaping on the shuttle at first is because it does not accommodate four crew members. When she later changes her mind after they've destroyed Ash, the natural assumption is that the shuttle has become a viable option now that they're down to three, but we later see that wasn't actually the case, because it only has two cryotubes. A better argument, I think, is that at that point they simply no longer cared.
Other mistake: When Dallas is in the air vent, his and the alien's location are both being tracked with the movement sensor held by Lambert. Whenever he crawls, his movements match up with the sensor. As he climbs down the ladder, his movement on the sensor goes downwards as it keeps in sync with Dallas himself and also shows that anything sensed on the sensor would be lower down on the sensor's monitor if someone or something was located on another level of the vent. The shot after Dallas says "Am I clear Lambert? I want to get the hell out of here" shows the monitor on the sensor and we can see the alien approaching Dallas on the monitor, with both Dallas and the alien on the same level on the air vent. Dallas then climbs down another level, and it is that the alien was in fact a level below Dallas. The problem with this is, if the alien was approaching Dallas from below, then the monitor should have showed the alien to be a few spaces below where it was on the monitor and not the same level as Dallas. (01:12:55 - 01:13:55)
Suggested correction: Simple, the sensor didn't work properly, or at least not as the crew expected it to. The tracker was made by Ash, based on "micro changes in air density." Ash was protecting the alien. It wasn't in his interests to make the sensor/tracker effective and efficient. Ash didn't care if Dallas, who he might perceive to be the greatest threat to the alien's survival, died.
Continuity mistake: Near the start, when Dallas is at the entrance to Mother, one of the lights to his left, the fifth one down from the ceiling, is not lit. The next shot from inside Mother looking out shows that light is now lit. This exact same thing happens a second time when Ripley is entering mother later in the movie. These two scenes must have been shot at the same time. (00:08:20 - 01:18:35)
Suggested correction: That light totally had enough time to light between the frames, because it was hidden by the sliding door for a brief moment. Lights were lit one at the time, not all at once, so this one starts to shine just a little bit later than all the others, that's it.
I consider this a valid mistake and the correction is a stretch. The lights only took about 2 seconds to light up, but she's at the door for almost 3.5 seconds after they're on and the last light did nothing. Then in the half second it took the door to open, the last light is now on.
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.
Suggested correction: Weaver was actually allergic to the combination of glycerine and the cat hair specifically. Once they stopped using glycerine, she was able to work with the cat without any trouble.
Continuity mistake: When the ground crew prepares to leave, the captain tells them to take weapons. All three crewman are in suits with side arms on hips. These weapons are never seen the rest of the movie.
Suggested correction: With reference to the side arms mistake the weapons are seen, when Kane goes to look inside the egg before he is attacked he is carrying his side arm and holding it ready.
Stupidity: The Nostromo essentially is a detachable ship attached to a mining platform. After it returns and docks with the platform, much of the movie occurs in the platform section and not the Nostromo itself. The supposed reason they can't just blow up the ship is that the shuttle can't fit everyone. Why couldn't they just lure the alien into the platform, seal the ship, and then use the ship itself to escape? They could then blow up the platform to kill the alien.
Suggested correction: Dallas tries to flush the alien out of the air ducts and is presumably killed. Lambert suggests fleeing in the shuttle, but it cannot support 4 people. Ripley decides to continue with Dallas' plan, but before she does so, accesses Mother and finds out Ash was ordered to help bring the alien back alive. When confronting Ash with this, Ash attacks Ripley and is revealed as an android. The survivors then decide to go with Lambert's plan because now there are only 3 people. There is no error here.
