Continuity mistake: In the close-up shot of Mulder just before he shoots Barnett, his black ear piece disappears. (00:42:15)
Continuity mistake: It seemed strange that Mulder was surprised not to find the Arthur Dales he knew at his apartment, when in "Agua Mala," he learned that Dales had moved to Florida. (00:08:30)
Deliberate mistake: It's completely impossible that the sound of the tape(that sounds like "Fox Maytrink") is in fact "Your time has come,Killer".
Continuity mistake: At The Beginning when a man says: "We're not who we are", he says it differently when Scully watches the tape. (00:01:20)
Continuity mistake: When Ray is eating the sandwich, there is a large bite out of one corner just before he removes the foil. In the shot from behind after the foil is removed, the bite is only from one slice of the bread.
Born Again - S1-E22
Revealing mistake: When Scully is doing the exam on the dead guy on table, he blinks and breathes. (00:12:05)
Revealing mistake: During the autopsy, right after Scully has the vision of her daughter, the body of Paula Koklos can be seen to move (watch her hands and neck). (00:24:05)
Within (1) - S8-E1
Continuity mistake: When Scully points out the location of the last time they saw Gibson Praise, she points to the (real) Palo Verde Nuclear Plant, which is west of Phoenix. In 'The Beginning' the plant shown was the (fictional) Rolling Hills Nuclear Plant, 60 miles east of Phoenix. (00:37:30)
Continuity mistake: In "Firewalker," Mulder reports that the day is November 11 and that he and Scully ended up in a 30-day quarantine. Scully reports that the date for the autopsy in "Irresistible" is November 14, which conflicts with the quarantine. (00:20:40)
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: When they find the felled ancient tree, the stump that Mulder clambers up onto to investigate the growth rings has a distinctive crack at the center and the growth rings are irregular in shape. However the stump that we get a close up of has no crack and regular circular rings. (00:18:20)
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)
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)
Fight Club - S7-E20
Continuity mistake: Scully tells Burt that Betty lived in a blue house and later tells Mulder that she found Lulu, who lived in a pink house. Betty actually lived in the pink house and Lulu lived in the blue one. (00:00:30 - 00:13:25)
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)
Continuity mistake: Krycek & Mulder leave FBI Headquarters, to go to Skyland Mountain, in a blue sedan - only in the next sceene - as Mulder is driving and almost falls asleep, the color of the sedan has changed to maroon. (00:12:40)
Plot hole: When Scully enters the game room after the game has shut off and the Lone Gunman are there but Mulder is missing. She is told that the only way in/out is from the door she came in. Later we find out that the bay that players use to enter the game is at the other end of the room and not conected to the door Scully used. So how did Mulder and Scully enter the game from the bay when the game was running?
The Lost Art of Forehead Sweat - S11-E4
Continuity mistake: When the camera shows Reggie Something from behind, he is shaking his head. However, after the cut, his head is static. (00:17:20)
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