At the end during the final countdown in the fight scene between O'Bannon and the possessed guy, the same filmed sequence is used three times, while the timer is between 3:30 and 3:00 remaining. First, opponent leads with a right that misses, then a left, then knocks down O'Bannon with elbow to jaw. They then fall down, wrestle a bit, and O'Bannon gets on top. This is re-used ten seconds later. Then again a third time, only shot from a different camera.
During the fight scene between Bannon and Waters, the editor used the exact same sequence from two different camera angles. In a close shot the actors take a few swings, then Waters connects knocking Bannon down, then the two start to wrestle on the ground. The exact same scene is shown from a mid-range shot.
During the final fight, the root structure base becomes exposed and shows the glass fibre matting used in construction and ends before entering the ground.
The alien radiation producing machine on the mountain has a radiation warning sign. As if they would warn us by using our human radiation sign.