Continuity: When the dead facehugger falls onto Ripley in the medical room, it lands on the floor with its legs up. The distant shot shows its tail has looped under its body, but the close-up shows the tail entirely straight. Submitted by wizard_of_gore

Visible crew/equipment: After Ripley fails to shut off the auto destruct sequence, she runs through a corridor filled with gas. As she exits from the gas right before the shot cuts away we see her pass by a full sized light. Beside this light is the clear arm and head of a lighting crew member. (This is acknowledged on the DVD commentary). Submitted by wizard_of_gore

Revealing: When the crew are searching for the missing face-hugger in the medical bay, Ripley's shirt can be seen to move to her right just before the face-hugger lands on her - indicating the puppet to be connected to her by a wire.

Audio problem: In the scene where the crew are dining together just before Kane meets his grisly end, the scene cuts from a long shot, where Parker is saying something, to a closer shot, with the conversation continuing as before. The problem is that Parker's voice can still be heard, but his lips aren't moving.

Revealing: Parker had hair. When the alien bit through his head the melon they used did not have hair. Also, the seeds can be seen inside the melon when paused at the right moment.

Revealing: When Parker shoots the blowtorch at Ash, Ash's face begins to melt off. When the skin melts off we see, in slo mo, that the dummy they used has a sealed mouth.

Revealing: They use the same shot three times when showing the acid eating throughout the ship. After the try to cut the finger off of the face sucker, acid begins to burnt through the decks. When they have gone down 1 deck and look up the see where the acid came through. This is shown at 0:39:50. They then move down 1 more deck and look up again. The acid is just beginning to burn through. Then they look up again and it is the same shot that was used before. The same hanging acid on the right with the drip on the left. This is at 0:40:20. After the acid has neutralized, they look up at the hole. It is the same shot again at 0:40:57.

Continuity: When Ripley is in Mother, you can almost read the words on her face as if a small projector is beaming these words on her. The screen she is looking at has 4 lines of green text. The image on her face is 1 line of white text.

Revealing: In the scene were Ripley is in the escape pod and has the space suit on, she hits the button to open the door and blow the alien into space. It is most easily viewed in frame by frame mode on DVD, but if you look at the shot were you see the alien getting sucked backwards you can see the wire coming out of its back.

Continuity: It can be seen multiple times throughout the film towards the end that there is no cat in the box. This is best seen when the front or back of the box is toward the screen when Ripley is moving down a corridor.

Continuity: In the scene where Ripley fails to override the self-destruct system she hits the computer with her flamethrower. As this happens it cuts to the screen which displays 10 minutes left until detonation, when really it's under 5.

Revealing: As Ripley stumbles away from the self-destruct system, The cooling rods are not visible. A few seconds later, in close-up, they can be seen to be above the edge of the compartment they are in.

Other: When the crew split into two teams of three, Ash gives Ripley a movement sensor, which he tells her detects movement in the direction its pointing. However, when Ripley points the sensor at Brett and Parker (who are both moving at the time) it doesn't detect their movement.

Revealing: When Ash attacks Ripley and Parker beats him off, the android gets up again and tackles Parker. Look closely as Parker crawls up against the wall...the body of Ash isn't a body at all...it's half a mannequin that doesn't even have a lower body connected to it, and it is visible when Parker's legs spread and you can see that there is nothing under Ash's torso except a big hole where the lower half should connect.

Continuity: In the infirmary scene where Ash, Dallas, and Ripley are looking for the facehugger that has detached itself from Kane, just at the moment when Ripley is looking under the table where Kane is lying, Dallas is empty-handed, he knocks something over and gives Ripley a fright and says sorry while at the same time holding a light in his right hand that was not there a second or two earlier.

Audio problem: When Ripley goes down to check out how Brett and Parker are doing with the repairs, she says: "Don't worry Parker. (pause) You'll get whatever's coming to you." In the short pause between these two sentences, you can hear Ripley say something like "You have". It seems to be a wrong line which has been deleted, but not properly.

Factual error: When Ripley is talking to "mother" by typing, it types "Emergency command overide 100375". "Override" should be spelt with two R's.

Factual error: When Ripley is trying to set the detonation of the Nostromo, the sequence begins before she activates the fourth and final fuse on the self-destruct control panel.

Continuity: When Ripley is setting the ship's self-destruct mechanism she goes to a panel in the floor. In this panel there are four holes with four screws next to them. When she inserts the first screw she has to manually lift up the cylinder to activate it. It also makes a sound as it is lifted. After she inserts the screw into the second cylinder it cuts to a view in front of her. The cylinder makes the same sound as it raises, but Ripley is not lifting this one. Her arms are doing nothing. When she activates the last cylinder she once again has to lift it up manually by the inserted screw. Based on the design of the mechanism it is apparent that all four cylinders have to be manually lifted, but Ripley does not lift the second cylinder. It lifts itself.

Audio problem: When Tom Skerritt first "interfaces" with Mother after being awoken, he says, "Good morning, Mother" - it is not even close to being Tom Skerritt's voice.