Continuity mistake: When Mulder pulls the nail from Blockhead's nose, the pliers are at The End of the nail, but in later shots it changes to the middle and then back to The End.
Visible crew/equipment: When Mulder and Scully are talking to the owner of the trailer park and he is berating Mulder, you can see the edge of the lens in the upper left corner of one shot. This is because the lens used was of a wide angle almost fish-eye type and the edge of the lens itself can occasionally creep into the frame on most cameras.
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