Revealing: In the scene where Newt is sliding across the grated floor, Bishop reaches out to save her and you can clearly see he's standing in a hole to make him look cut in half.

Continuity: In the scene where the Marines first enter the reactor room, the "Mission Time" readout on the shoulder mounted cameras jumps backwards and forwards in time with every cut.

Continuity: When Bishop is impaled by the Queen alien he spews android fluid/juice all over his chin. In a subsequent shot his chin is clean and he is spewing fluid again. The following shot his chin is once again covered.

Continuity: In the end of the film, when Ripley pulls the Alien queen down in to the hatch we can see that the bulb on top of the machine cracks but when they are lying on the hatch the bulb is whole.

Continuity: You may need slo-mo to see this: towards the end of the film, when Ripley is going down in the elevator to save Newt, pay close attention to the indicator screen counting off the floor numbers as they pass by. It goes floor 8, 7, 6 then 7 again and then 5.

Continuity: When Ripley and the Queen fall into the airlock, look closely at the Queen's tail. It seems that the sharp end of it is broken off, or missing. Later on in that scene it is back.

Continuity: 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.

Continuity: Director's Cut: During the briefing scene on board of the Sulaco, Lt. Gorman begins the briefing. He gets interrupted by Hudson. Before the shot changes to Hudson, you can see Gorman standing straight in front of the marines and looking straight ahead. In the shot from Hudson, you can see Gorman looking to the right to face Hudson. He still should be looking straight ahead. Submitted by Christoph Galuschka

Continuity: When Ripley and Hicks are discussing their defence plans after the first encounter, they decide to put one of the auto guns in each of three locations, leaving one left over. When we see the guns in place they have actually used two guns in each of two locations, that is, two pairs.

Plot hole: Director's cut: When the autoguns were mowing down the army of Aliens coming through the service tunnels, there should have been enough acid blood being sprayed out to melt a massive hole in the tunnel. But the acid has no effect at all on the tunnel walls.

Continuity: During the Cargo Loader vs. Queen fight, Ripley grabs the Queen and it closes around her neck. In the next shot it is closed around its head. It changes extremely quickly; therefore it couldn't have changed position.

Revealing: When the autoguns fire at the aliens for the second time, there is a flashcut of an alien being blasted apart. Watch closely; it's the same clip of the alien that Vasquez shot and subsequently sprayed Drake with acid.

Continuity: In the sequence when the APC is fleeing the hive, and the alien punches a hole though the windshield to get to Ripley. The hole disappears in the next shot when the light reflects off of the glass.

Continuity: There are many holes in the 'squad structure' once the marines arrive at Hadley's Hope. Gorman calls up 1st Squad (comprised of Apone, Vasquez, Crowe and Hudson) to approach the colony first. They do. But, if you look closely, there are other marines present. When they arrive at the door Apone goes straight to the console, Hudson holds back to our left and Crowe rests in the background on the right of the screen. Apone then calls Hudson up to do a bypass. If you look closely as Hudson runs up to the console you will see Frost in the background, he steps up to the left of Crowe (his left) and on the left of the screen, you will see Wierzbowski crouch with his flamethrower, slightly obscured by Vasquez (look between her legs). Then 2nd squad is called up. It is comprised of Hicks, Dietrich, Drake, Frost and Wierzbowski. Watch the shot of Vasquez entering the lock and you will see Frost standing roughly where he was when the 1st Squad ran up. Clearly the original scene had all the marines descend on the North Lock simultaneously. The confusion continues when Gorman, Ripley, Burke and Bishop enter the South Lock. They meet up with Hicks' squad yet Dietrich and Wierzbowski are curiously absent.

Continuity: At the beginning of Aliens, when the door is cut through, the markings and lettering on the transparent cover of Ripley's suspended animation pod are different from those that were on it when she was asleep at the end of Alien.

Revealing: When Vasquez goes to weld the piece of pipe back in place part of it has already been welded. Look at the right of the screen. The piece has already been tack welded before she fires up the torch.

Other: When Ripley shows off her skill with the power-loader, another walks along in the background. Look carefully, it's Ripley driving.

Revealing: In the scene where Ripley rescues Newt, there comes an alien from a corner and it jumps from side to side. In the second jump, you can see two wires on its back.

Visible crew/equipment: In the Reactor Room scene, where the Marines first encounter the aliens, there's a part where Dietrich is grabbed from behind and accidentally ignites Frost with her flamethrower, causing him to fall down the stairwell.  As he's falling, if you look, you can see part of a leg and a cable belonging to one of the technicians on the set.

Visible crew/equipment: In the scene at the colony when a large vehicle approaches the camera, the reflection of someone's face can be seen showing the true scale of the miniature.