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. (Timecode)
Aliens (1986) - 2 with pictures
Directed by James Cameron, starring Bill Paxton, Lance Henriksen, Michael Biehn, Sigourney Weaver
Screenshots of mistakes are only visible to members, but there's a free picture of the day, updated daily, and the top 30 screenshots are accessible too.
Other: When Ripley shows off her skill with the power-loader, another walks along in the background. Look carefully, it's Ripley driving.