*- The “beacon” that the Nostromo homed in on in Alien (1979) and Ripley refers to at the inquest would have been heard by the space ship that carried the colonists to the planet, or the supply ships, cargo ships, etc.; yet it remains undetected or of little interest to anyone or any other spaceship for 57 years.
*- During the inquest, Van Leuwen refers to Ripley’s company ID number as NOC14472 while the data screen in the background displays NOC14672.
*- Obvious looped background conversation noise during the breakfast scene.
*- Marks are seen on the tabletop before Bishop starts the “knife trick.”
*- In the first wide angle shot, Bishop is stabbing the knife behind Hudson’s hand.
*- A foot is visible when Frost falls down the shaft.
*- The marines can stand up straight inside the APC, yet are taller than it when outside.
*- Ripley’s headset changes position around the time she tells Gorman “they’re cut off.”
*- During the investigation of the power plant, Lieutenant Gorman informs Ripley that the M41A Pulse Rifle fires “ten millimeter explosive-tipped caseless” ammunition. However, during the sequence in which the survivors retreat from their makeshift base, shell casings can clearly be seen coming out of the rifles, particularly in the shot where Vazquez runs out of ammo.
*- The APC window becomes unshattered right after it squashes the Alien.
*- When the marines exit the APC and enter the alien hive, they go down several flights of stairs. When Ripley drives the APC into the alien hive to rescue them, it can be seen that she is going down a ramp.
*- When Ripley tries to break the glass in the med lab there is a scuff mark on the glass before her first swing. After this finishes, the mark disappears and we see Ripley actually making the mark with her second swing.
*- As soon as the Alien snatches Newt, the motion detector stops sounding.
*- When Ripley retrieves some weapons to rescue Newt, she picks up one weapon from the rack, puts a different one down, picks up the second weapon from the rack, and puts the first one down on the floor. This is fixed in the special edition.
*- When Ripley meets the queen, there is a scene where the breathing sound and the steam coming out of the queen’s mouth are out of sync.
*- The yellow caution light on the loader when the mother alien pulls it into the airlock breaks and unbreaks.
*- The Alien Queen’s tail spear vanishes while she is in the airlock.
*- The hole where Lance Henriksen’s body is can be seen when Bishop stops Newt from being sucked out of the airlock.
*- The acid blood of the aliens rarely seems to damage the walls and floors like it does in Alien (1979). This is especially noticeable in closed spaces like the air shafts, APC, and elevator, where the people get burnt but nothing else does.