Three Words - S8-E16
Continuity mistake: When Mulder sits at the computer terminal in the census records room, we see two empty boxes on the screen, one for an ID and one for a password. The shot cuts to Mulder, then back to the screen and shows him typing the password, while the ID has already been typed in; it is very long and there wasn't time in between shots or nearly enough clicks of keys for Mulder to have entered that ID.
Answer: As he stated many times throughout the series, Mulder needed Scully to be sober and skeptical. Whenever Scully's skepticism wavered and she started questioning her own rationality, Mulder would try to restore her sense of skepticism, because he needed her to be clear-thinking.
Charles Austin Miller