Other mistake: Near The Beginning, we see security camera footage from a computer watching Drake type a letter about cancelling the COS project. The footage is too low to be shot by the security camera. It's the regular camera that continues the scene since there is a cut to it from the monitor (and the shot pans to the right before Drake is killed). Many TV shows and movies forget to line up the POV shots from security cameras, using the real footage instead.
One Breath - S2-E8
Other mistake: At The Beginning of the episode, a gravestone for Scully is shown. However, it seems as if less than a week passes between Scully's mother and sister deciding to let her go and Scully waking up. It's unlikely that the gravestone business would have the stone ready in such a short time.
Revealing mistake: When Edward aims the rifle out of the window, you can see the cap is still on the scope. (00:40:22)
Revelations - S3-E11
Continuity mistake: Kevin's mother uses her car to hit the 'devil' and shatters the bottom right of the windscreen. The following shots, including the crash into the ditch, show the car with the windscreen undamaged. (00:28:59 - 00:29:22)
Visible crew/equipment: After talking to the scientist about his car, Mulder and Scully are talking in front of a door. In the glass of the door is a reflection of a third person.
Continuity mistake: When they find the cocoon, the body inside is completely different in appearance from one shot to the next shot of it.
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)
Deep Throat - S1-E2
Visible crew/equipment: When Mulder and Scully attempt to interview Col. Kissell, as he gets out of his car, you can see a square light reflector screen reflected on the car door. (00:12:37)
Continuity mistake: During the Re-qualification practice shoot scene Dupre as agent Willis fires until he suffers a failure-to-eject stoppage (stovepipe), despite staring at the ejection port throughout the preceding drill he fails to recognise and clear this (as any firearm user would, especially a bank robber with the partial memories of an FBI agent/instructor), and could potentially still have rounds in the magazine. At the next camera change the slide is fully back despite no manipulation from Dupre, as he removes an empty magazine. (00:19:01)
Unrequited - S4-E16
Factual error: By its uniforms, rank insignia (i.e. point-down chevrons), drill and instrumentation (e.g. tubas instead of sousaphones), the military band performing at the re-dedication ceremony at the Vietnam War memorial in Washington is a Commonwealth (probably Canadian) band and not an American band. Unlikely at a formal military ceremony in the United States.
Other mistake: This episode establishes that whenever Pinker Rawls passes through solid matter, his clothes remain behind, as anything he is wearing does not share his ability. However, late in the episode when Jackie throws the pot of boiling hot soup at him, the soup is shown to completely pass through his shirt, when it should have stuck to his shirt instead.
Continuity mistake: While Mulder is picking himself up in the synagogue's attic after being pushed/tripped, you can see that his gun is unloaded, with no magazine. (00:25:07)
Character mistake: Scully gives a description that Eve is driving a Blue Carolla. However in the next scene, Eve is driving a Pontiac, not a Toyota. (00:28:00 - 00:28:51)
Factual error: The local Pasadena station code is WXDL, however it should start with a K not a W. (00:00:05)
Revealing mistake: At The Beginning of the episode we see Duane being abducted and he begins to scream. Look at the "alien" on the left of the screen near to the top of the bed and you will see him move his head revealing where the suit ends and neck/head begins. (00:02:12)
Continuity mistake: Towards The End of the episode there is a scene where Mulder is talking to another agent next to an ambulance and it is shot at night despite it being morning only a couple of seconds ago. (00:33:53)
Continuity mistake: At The End of the episode, when Lyle is transforming in the bathroom, we see his hand perfectly shred a shower curtain, however in the next shot we see his hands and they are still fully human. There's no way he could have done that. (00:38:44)
Continuity mistake: During the very beginning of the episode when the cop and researcher are talking on the shore they go from facing each other to the cop facing the lake and having to turn his head to talk to the researcher between shots. (00:00:30)
Continuity mistake: Scully pushes Pfaster into the bathtub and he gets out soaking wet however when he leaves the bathroom and begins to chase Scully around the house his clothes are bone dry. (00:41:20)
Revealing mistake: When Mulder, Scully and the other agent are looking at the covered body of the dead prostitute if you look closely you can see her chest rising and falling. (00:17:22)
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