Continuity: When Mulder is in the tower and Scully has just found him the sweat patches on his shirt change in between shots.

Factual error: The Arecibo Radio Telescope is abandoned when Mulder goes there. However, after SETI was cancelled, the telescope was still used for other things.

Continuity: When Fox Mulder is having the flashback when Samantha was abducted, he looks at the doorknob, in the close-up he is still looking at the doorknob but it has changed colour.