Continuity: Just after the doctor started the post mortem on that little girl, the front of his gown is covered with blood. Yet, a few seconds later, after the two other guys appeared, his gown looks better, with less blood. And during the whole post mortem scene, the blood spot actually changes its size a few times.

Continuity: In the scene where Ripley just got out of the shower and is talking to the one guy she is wet, then the camera cuts off her and goes back to her and she is completely dry.

Other: The alien that comes out of the dog is a lot bigger than the actual dog just seconds after it appears. This only applies to the theatrical version, as in the extended version the alien comes out of an ox.

Revealing: In one scene, two of three prisoners get killed by the alien. The last one is sprayed with blood and tries to escape in panic. With his left arm, he leans upon a half-open, hydraulic-powered metal door. However, it moves a little to the left, and as the prisoner takes his hands off, it immediately snaps back to the right. Now even if you suppose that there was no hydraulic pressure behind it, it should not have moved to the right again. It is very obvious that this door is just a light-weighted part of the scenery.

Audio problem: When Aaron attacks "Bishop II", he yells, "F***in' android.", but his lips hardly move.

Continuity: In the cafeteria scene, Ripley gets a square of what looks like cake and pours half a glass of orange juice. When she sits down her glass is full.

Audio problem: Right before the people from the company enter the prison, Jude is being chased by the alien and yells, "Dillon, help me. Please." When he yells, "Please.", his lips don't move at all.

Continuity: As Ripley and Dillon lure the Alien into the piston chamber, Morse closes them in just in time. Watch closely - he misses the switch.

Continuity: After Clemen's death, there is a shot of the ventilation shaft into which he was dragged by the alien. However, the shaft seen is the one in which Andrew's is taken into by the alien later. You can tell the difference because of the ceiling colour and the design of the ventilation shaft.