Continuity mistake: In The Beginning, when the Bounty Hunter gets out of his car, Jeremiah Smith says nothing. However, in the same scene at 42:08 in the "Talitha Cumi" episode, Jeremiah says "He is here to kill me." (00:00:05)
Continuity mistake: Scully tapes an X in the window,that X changes shape when Scully is talking to Mr. X and before Mr.X dies when he checks on the apartment.
Continuity mistake: Jeremiah Smith and Mulder are with the kids, and in the background, when CSM is looking through the window, Samantha's clone and the other kid disappear.
Other mistake: When the attackers leave the sheriff's house they walk and run as normal people, although in previous scenes they walk in a clumsy way. The same in the scene with chasing pigs. (00:23:00)
Visible crew/equipment: During the scene when Mulder, Scully and the deputy approach the farmhouse there is a moment when Scully walks up to a chicken coop and a boom microphone with a fluffy wind cover on can be seen coming up from the bottom of the screen (Underneath Scully). (00:30:35)
Audio problem: Scully asks the deputy if the vests are necessary and he replies in the same scene. His mouth is way off from his reply. It's likely this is because the show was shown on 4:3 aspect ratio televisions at the time, and he would simply not be visible. Because the show was shot in 16:9, he is very much visible on modern televisions and the mistake is incredibly obvious.
Factual error: A 747 jumbo jet is shown in the first scene of the episode. Later we can see the aircraft cabin with a 3X3 seat configuration. However, there is no 747 with such layout. (00:01:40)
Factual error: The episode is supposed to take place in Traverse City, Michigan, United States. Mountains are visible in the sequence when Mulder is chasing after the killer on foot. The show was shot in Vancouver, British Columbia.
The Field Where I Died - S4-E5
Continuity mistake: When Scully is searching through the pictures to find Sarah Kavanaugh and Sullivan Biddle, she turns the photographs over and they have a label on them to say who they are. Yet when the shot changes angle to show the photos from the back, the labels have disappeared.
Sanguinarium - S4-E6
Revealing mistake: When Mulder and Scully enter the doctor's house, you can see over their shoulders that it is showering with rain outside, yet both of them are bone dry.
Musings of a Cigarette-Smoking Man - S4-E7
Character mistake: Ramón Mercader did not assassinate Leon Trotsky with an ice pick, as Frohike claims, but with an ice axe. (00:03:00)
Musings of a Cigarette-Smoking Man - S4-E7
Factual error: In the US classified information system there is "compartmented information", but there's no "compartmentalised information." (00:08:00)
Musings of a Cigarette-Smoking Man - S4-E7
Other mistake: When the CSM is aiming at the door, it must be quite difficult for him because it seems that he forgot to take off the protective lid from the night vision rifle sight. (00:35:10)
Musings of a Cigarette-Smoking Man - S4-E7
Other mistake: In the episode "Musings of a Cigarette Smoking Man," when CSM is writing his letter of resignation on his typewriter, you can see that the letters are already there - he is simply typing over them. (00:39:30)
Musings of a Cigarette-Smoking Man - S4-E7
Continuity mistake: In other episodes the name of The Lone Gunmen's newsletter is "The Lone Gunman", but in the shots of their office door it has a sign saying "The Lone Gunmen. Publishers of 'The Magic Bullet' newsletter." (00:43:10)
Musings of a Cigarette-Smoking Man - S4-E7
Revealing mistake: As the smoking man sits on a bench after finding out his story was rewritten, there are mountains visible in the background. Atop one of the buildings in the background is a Canadian flag waving in the wind. This show was shot in Vancouver, but is set in Washington D.C. There are no tall mountains that close to D.C.
Tunguska (1) - S4-E8
Factual error: This is probably the first time in history of civilized mankind that a person with a diplomatic visa is full-body-cavity searched, not to mention the illegal opening of the diplomatic bag. (00:04:05)
Factual error: The last number on the truck's license plate is "77." On Russian plates the last two/three digits stand for a registration place. "77" is a number for Moscow, but the Gulag is located in Krasnoyarsk region, so the number should be different. Besides, the format of the plate (LDDDDL|DD) is incorrect - the correct one is LDDDLL|DD (L - letter, D - digit). (00:11:05)
Continuity mistake: The truck stolen by Mulder from the Russian labor camp is Unimog 406. However, during the accident scene, when it comes out of the woods and falls from the hill, it miraculously turns into Unimog 404 model. (00:13:30)
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