Alien (1979) was scripted to have a scene where the xenomorph was almost trapped by Ripley and Parker in the airlock of the ship’s “B” level. It escaped but lost a limb in the process, leading to its acidic blood causing critical decompression. Due to budget restrictions, the scene was not completed, but here is a partial moment of Lambert reacting to the situation, which was filmed before the decision was made to leave out the scene entirely.

Alien explained (1979) - Film Colossus

Alien deleted scene 1