20 Things You Somehow Missed In Alien
8. The Wrong Trousers
As the creature takes out both Parker and Lambert in one horrifying sequence, a bizarre but noticeable piece of editing famously crops up. Specifically, that as its tail moves between Lambert's legs, the clothes in the shot don't even remotely match up with what she's wearing and, in fact, belong to Brett.
This was because both deaths were originally storyboarded and filmed much differently, with the Xenomorph dragging Brett into the ceiling with its tail (hence the shot) and Lambert escaping only to then die of fright hiding in a locker. When both were tweaked, Scott decided to include the shot from the former in the cut of the latter to make up for the fact there was no footage of Lambert being physically attacked.
He just assumed nobody would notice the costume problem.