Continuity mistake: During the scene where Ripley is trying to break the window with a chair, there is a scuff mark on it before she hits it. It goes away and comes back. (01:32:15)
Suggested correction: The view from Ripley's side is looking up at the window and from the other side level where there are reflections at the same height (using Ripley as a reference) of the scuffs. There is no way to tell if the scuffs are there or not.
The Director's Cut (and maybe even on the theatrical version) on the 2010 Blu-ray removes the scratches, so I assume they were not supposed to be there initially.
Revealing mistake: When the swarm of aliens drops through the ceiling panels, you can tell that Ripley and the marines don't have magazines in their rifles. It's especially visible when Ripley looks up before Hicks raises the panel and sees the aliens.
Factual error: If you damage a fusion reactor, it doesn't explode with a thermonuclear effect. It just shuts off.
Suggested correction: Actual fusion reactors don't exist, yet. Certainly not this size. You have no idea how this reactor works. It's not unlikely it uses fissile material to operate.
Stupidity: After the ammo is removed when the team are under the reactor coolers Vasquez is still on point, even though her machine gun doesn't have a flamethrower capability and her hands are too occupied to be able to use one. Should have been replaced by another team member with an 'active' weapon.
Suggested correction: True but Vasquez's weapon is a) still loaded/powered and b) has a sophisticated sensor system which might be better at detecting enemies than naked eyes. It's still a stupidity because even if she sees something she shouldn't be able to do anything except call it out (as far as Gorman and Apone know) or fire (which is what she and Drake actually do, against orders). But at least it's a logical stupid mistake, instead of a senseless stupid mistake.
Other mistake: They should have had much more than only twenty-six minutes to save Newt. Bishop said that the reactor would blow in four hours after seeing the emergency venting. He said it would take forty minutes to crawl down that pipe, an hour to patch into and align the antenna, thirty minutes to prep the ship, and fifty minutes flight time. 40+60+30+50=180 minutes, gives them an hour spare.
Suggested correction: And how are you so sure everything went smoothly without problems? Any of those things could have taken longer, leaving only 26 minutes.
