Revealing mistake: When Scully grabs Mulder's hand, his watch shows 11:25 AM, but when the agents enter the house, the scene's stamp reads "Phoenix, Arizona, 4:58 PM." (00:17:55)
Revealing mistake: When Mulder - whilst trapped in the body of Morris Fletcher - is doing various poses in front of the mirror, several of his movements and the corresponding movements from the realized reflection of Morris Fletcher are slightly out of sync with each other.
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