filming. He set up the facehugger on the table leg,  then dragged it off and later edited the piece of film to play  backward to make it appear to be moving forward towards Ripley. Crew  thought that the fact that water was falling down during this whole  scene would affect the sequence that was filmed backward (it would  show the water moving up instead of down). In the end, the water was  not visible enough to see the direction in which it was falling.