When Ripley interfaces with Mother for the first time and sees the special order, an instruction reads as "Insure return of organism" rather than "Ensure return.," a common enough grammatical error for humans but not one that a programmed super-computer would generate. This mistake occurs on the same screen where the word 'override' is spelled incorrectly but this observation has already been posted by another contributor. [Programming error. Computers don't know "words," just programming codes. If the original programmer was a bad speller, so might the computer. Case in point: "All your base are belong to us."] Corrected by JC Fernandez

When Ripley is in Mother there is a moving shadow of a crew member over her right shoulder in the doorway. This occurs after Mother responds "unable to clarify". [No error here. Once Mother tells Ripley the true nature of the mission, we see Ash is now seated next to Ripley. The previous shadow movement was Ash sneaking into the room.]

Normally the face sucker alien is helping the host, Kane, breathe. This is evident by the close up shots where the sacs on the side of his body pulsate. In the panoramic shot the sacs on the side of the face sucker are not pulsating. [NO one ever said they were pulsating specifically to give Kane air. While it's probably giving him air in some other way, the pulsating is probably just the facehugger ejecting the alien embryo into Kane, which it would only have to do for a little while as iopposed to helping him breathe.]

When talking to 'Mother' the characters never seem to type enough keystrokes to account for the wording of their questions on the computer screen. [Who's to say in the future they don't have "short hand" software for quick typing?]

When Kane enters the derelict ship and looks around, we see everything from his point of view. One of the eggs on the left has some sort of box behind it, which looks very much out of place, perhaps something the props department left behind. [It's a derelict ship. We don't know what is supposed to be where on the ship. A box may not be out of place, besides which anything could have been moved or pushed aside by the alien, or by crewpeople trying to escape the alien. There are any number of reasons a box may be out of place, most of which don't involve the props department.]

It's difficult to see, but the instructions for self destruct (at least those for cancellation) appear to be in French. (Although fleeting, this is easier to spot in the cinema than on DVD) [While the instructions on the right side of the panel are in French, they are simply translated versions of the instructions on the left, which are in English.]

Ripley was originally supposed to be a male. The decision to cast a woman was done on a lark, and no script changes were made to "feminize" the character. [Dan O'Bannon's original screenplay never mentioned sexes. All the characters were written to be either sex.]

Ripley's nosebleed: from 1:17:16 (chapter 14: 'A Confrontation with Ash' on the '99 DVD), Ripley's nose starts bleeding, eventually very noticeably. This is almost a full minute before Ash begins attacking her by throwing her twice, which might actually make it bleed. [This would only be an error if a later scene were intended to show the moment the bleeding is caused by some physical strike, but there's no such moment (and there is the chance that her first shoving match with Ash may have had her head striking his, but it's not a certainty). Still, nosebleeds are commonly triggered by stress in people prone to them. Ripley's nosebleed begins after she learns of the special order (crew expendable) and becomes extremely distraught- and after her physically tossing Ash around (causing his head cut that later drips). She marches off, and in the passageways she can then be seen with the nosebleed.] Corrected by John W Rosa

When Brett is about to be killed by the alien, a close up shot of just his hat is shown when the alien's teeth impale his skull and his brains come pouring out. In slo-mo you can see that an alien hand is holding his head in place as it strikes. A split second later we see Brett's face, but there is no hand anywhere near him nor is the alien reaching out towards him. [No, the alien DOES have its hands on his head. It is on the very left of his hat, and is very hard to see, but it is there.]

When the crew goes into the ship with the eggs in it, you can clearly see that all their gloves are hockey gloves just painted over. Pretty cheap. [Just because they look like hockey gloves (and probably were used to make the gloves) doesn't mean they really are in the movie. Maybe in the future, all astronaut gloves look like that.]

When Brett is looking for Jonesy (the ship's cat), prior to being killed by the alien, there is a scene as he passes through one of the doorways when the boom mike is clearly visible in the top of the shot. This is from a video viewing. [It does look like it's a boom microphone, but it's actually just Brett's shadow. You can tell by watching the shadow that appears on the door right as he approaches it.]

Take a close look at the masks they are using when they remove the helmet from Kane. The masks they are using to prevent contamination are nothing more than ordinary oxygen masks that one uses at a hospital. This is evident by the hose receptor on the bottom of the masks. In reality these masks would not prevent them from catching any airborne disease that this alien would have. I know they are in a infirmary, but a space ship would/should be better equipped in case it comes in contact with other life forms. [While these look similar to current masks, they are part of the highly advanced and miniturized technology of the time - they can do whatever they say that they do.] Corrected by Myridon

When the face sucker alien jumped at Kane it only attached itself to the front of Kane's mask. It did not penetrate the mask. When they get Kane to the Nostromo, the face sucker alien is completely inside his mask and there is a big hole that it entered through. [The face-hugger used an acidic excretion to burn its way through the helmet visor. The visor can be seen to be warped by the effect of the acid.] Corrected by Tailkinker

When the face sucker jumps at Kane, he only jumps onto Kane's helmet. This is best seen when in slo-mo on the DVD. Having it jump through his helmet, as we are led to believe, would have resulted in some glass breaking and facial lacerations to Kane and injury to the face sucker alien. [The face-hugger emits a quantity of acid and burns its way through the helmet visor. The visor is visibly affected - the sides of the hole appear melted, not broken.] Corrected by Tailkinker

Technically speaking, it is impossible to detect the Alien by micro-changes in air density. This is because the device would constantly be reading the mass(i.e. density) of the air molecules around it, and any movement would set it off, as the air molecules would be moving. Even breathing would set the device off. [Ash explained the motion tracker with micro changes in the air density. It was deceiving the crew all along. When using the motion tracker. Ripley notices it works differently, an unknown way and says, "Micro changes in air density, my ass."]

When Lambert, Kane and Dallas are on the alien ship, before they find the alien corpse I think, you can see jets of gas coming out of their helmets, which is supposed to be them exhaling. Only Lambert doesn't appear to be breathing. Poor lass. [We see her breathe several times during the scene. The times we don't? Well, they were in an exciting, scary, suspenseful situation, and Lambert is not exactly fearless, so it is conceivable that she was holding her breath in anticipation of a turn for the worse.]

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. [Ash could have disabled the hydraulics of the door and then quietly pushed it open.]

The scene where the facehugger's acid blood eats through the medical bay's floor was done with actual sulphuric acid stained yellow. [It actually wasn't. A polystyrene mock up of a floor panel was made and doused with petrol, which dissolved it. Nothing as dangerous and unpredictable as real acids were used.]

The newborn alien that bursts from John Hurt's chest is next seen full-grown, munching on a crew member who is searching for Jones the cat. Assuming that it needs to kill to eat, how did the alien suddenly appear full-size without any nourishment? [There's one big false assumption there - that the creature kills to eat. The extended cut of the film shows that in at least two cases, members of the crew were taken alive to create new eggs, and in other cases, the bodies are left apparently uneaten. The aliens in the film series have always shown the ability to grow to full size extremely quickly; the mechanism is unknown but it doesn't involve eating other lifeforms as no alien has ever been shown to attack before reaching full growth. The most likely explanation is that the additional mass required is simply taken from whatever the alien finds around it (metal, rock, whatever) and is incorporated into the body structure in some unexplained manner (possibly involving the breakdown of such matter via the acidic blood and its reconstitution in a form that the alien can make use of by some organ within the alien body).] Corrected by Tailkinker

The escape shuttle used by Ripley and the cat is buffeted by a shock wave from the Nostromo's explosion, a shock wave that can't exist. In space, there is no medium through which a shock wave can propagate. [It's not a shockwave. She's just blown up a colossal ship behind her - what she's hit by is the vaporised remains of the ship, rushing outwards from the point of explosion.] Corrected by Tailkinker