Continuity mistake: When Scully finds out about Betts' mother she says that "She lives right here in Pittsburgh." Nothing wrong there except that at the time they has just left Chuck Burks' lab - which is in Maryland. (00:17:40 - 00:21:10)
Never Again - S4-E13
Continuity mistake: In the front shot Scully holds the photo with 2 fingers (thumb and index), while in the back shot she uses three fingers (thumb, index, and middle). (00:24:55)
Continuity mistake: When Mulder and Byers find Scully in Penny's room, there is a black stripe on the ceiling of the corridor, while in the scene when Scully is leaving the room there is no stripe there. (00:36:50)
Continuity mistake: While Mulder's waiting for Langly and Frohike to unlock the exit door, Gray-Haired Man keeps shooting at the glass door, and the increasing bullet damage on the glass doesn't stay consistent as more damage occurs, and changes between the closeups and wideshots.
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)
Continuity mistake: The wedding ring Ariel is holding in her outstretched hand is either vertically protruding from the palm of her hand or is hidden inside of it, depending on the shot. (00:40:25)
Unrequited - S4-E16
Continuity mistake: When Scully and Mulder run away from the dogs, the gate is fully open, while in the previous and next shot only the door is open. Plus their car standing in front of the gate is missing. (00:09:30)
Continuity mistake: During the handbrake turn Scully smiles, although in the preceding and following shot her face is very serious. (00:31:15)
Continuity mistake: In the shot of the 6th Precinct police station, it has a California state flag flying out front. The episode took place in Massachusetts, at the Massachusetts Institute of Technology. (00:07:45)
Continuity mistake: We see Scully wearing pants while sitting on the couch, but when the real Mulder comes in, she jumps up and we see she's wearing a skirt. (00:38:35 - 00:41:25)
Continuity mistake: During and just after the Mulder's seizure, when Scully's face is shown, it is at the level of a standing person which suggests that both agents are standing, but in the next shot Mulder and Scully are crouching. (00:31:35)
Continuity mistake: When the CSM discovers the bright spot on the carpet, he immediately realises that Mulder's apartment was under surveillance. However, one can notice that soon after entering Mulder's apartment, the CSM looks down at the floor and carpet covered with blood and there is no bright spot. (00:14:00)
Continuity mistake: During the meeting at a horse track, after the CSM says "You need my expertise, " the First Elder raises his head. In the following shot from the other side, he raises it again. (00:21:00)
Redux II (3) - S5-E2
Continuity mistake: Although the subtitle states 12:00 AM, Mulder's watch hands mark 02:35. (00:43:16 - 00:43:39)
Continuity mistake: When the Lone Gunmen speak with Susanne Modeski, in the background there are some cars parked in front of the Stadium Inn. However, just seconds after, when the telephone rings, there is a white truck parked at the entrance. Later on, the cars are back again. (00:38:55)
Continuity mistake: During the shootout in the warehouse, a wedding ring is visible on Mulder's finger. While it's possible Mulder was married before, the Lone Gunmen are shown hacking into Mulder's FBI dossier and Langly reads out that he is single.
The Post-Modern Prometheus - S5-E5
Continuity mistake: Izzy unwraps a peanut butter sandwich and sets it on a bare tree stump as bait for 'the Great Mutato', then he steps away with the others. When we see the Great Mutato hurriedly put it down, a paper bag is suddenly sitting on the stump beside the bitten sandwich.
Continuity mistake: Scully's FBI badge number that she gives to the phone company is different to the one she gives in season 4's "Teliko". (00:02:05)
Continuity mistake: The toxicology report lists the birth date of Mrs. Sim as 6/6/67 which would make her 30, but Detective Kresge says that she is 40 years of age. (00:03:45 - 00:14:10)
Continuity mistake: Mulder says that Scully was abducted and missing for four weeks. In "Duane Barry," the date stamp is given as August, then in "3," when Mulder returns to the X-Files office he turns the calendar all the way to November. Since Scully is returned the next episode after this, she must have been missing for at least 3 months, not 1. (00:06:20)
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