Factual error: When Mulder gives Scully the birthday card, she says that he is two months early. Given that Scully's birthday is on 23 February, the time of the episode should be sometime near Christmas. However, through the whole episode, there is no sign of Christmas time (not a single Christmas tree, no Christmas decorations, etc). (00:19:35)
Via Negativa - S8-E7
Revealing mistake: When Doggett examines in the car the body of Agent James Leeds, the carotid artery of the victim is pulsating. (00:05:40)
Continuity mistake: When Scully walks into Mulder's office, she stops in the position with the "I want to believe" poster in the background, then she takes a couple of steps to make acquaintance with Mulder, and she finds herself again in the position with the poster in the background. (00:05:15)
Continuity mistake: In the right shot Mulder picks the dirt with his fingers to the plastic bag, while in the left shot he pours it into the bag from the palm of his hand. (00:06:15)
Other mistake: After AD Skinner is finished being interviewed by the police, Mulder asks him about why he would employ the services of a prostitute. Skinner looks at him in shock and Mulder says "You didn't know she was a prostitute did you?" I find it hard to believe that at no point in the interview did the police not mention to Skinner the dead woman he woke up next to, after spending the night with her, was a prostitute.
Visible crew/equipment: As Scully rolls down the stairs with the killer at The End of the episode, once they reach the bottom a hand pops out from the left side of the screen.
Continuity mistake: As Lindquist holds the bag of evidence, it is hanging down in the fingers of his right hand. The next shot shows him holding the evidence bag in the palm of his right hand.
Audio problem: The first scene following the intro, when Mulder and Scully step out of the car, Scully says, "I still don't get it" but her mouth doesn't move. (00:02:30)
Continuity mistake: This is probably one of the most intriguing chess plays in the history of mankind. In the first move shown on the screen Gibson moves a white knight from e4 to f6. Then, in the close-up, the situation on the chessboard more or less corresponds to the arrangement of the figures previously shown on the screen. However, in the next shot, when we see the chessboard from the Russian perspective, the arrangement is completely different. Especially, there is no white knight on the chessboard at all. In the following shot the white rook suddenly appears on g8 (and is subsequently beaten by the black king), but in the next move Gibson again moves his white rook on g8, while the black king has miraculously returned to h8 and again beats the white rook. Moreover, Gibson could not play two white rooks, because later on we see that there is still at least one white rook on the chessboard.
Continuity mistake: During the handbrake turn Scully smiles, although in the preceding and following shot her face is very serious. (00:31:15)
The Sixth Extinction (2) - S7-E1
Continuity mistake: Mulder writes Kritschgau's name on the ulnar side of the palm of Skinner's right hand. Later when Skinner is looking for Kritschgau in his apartment building, the writing is on a different part of Skinner's palm, beginning around the middle and extending diagonally towards the thumb. (00:11:50 - 00:15:30)
The Sixth Extinction (2) - S7-E1
Character mistake: When Kritschgau is testing Mulder's remote viewing capabilities, he tells Mulder that he is at about 5% accuracy. However, Mulder got at least two right and not enough time had passed for him to have had 40 opportunities, so his percentage of accuracy should be higher than five. (00:27:00 - 00:27:45)
Continuity mistake: When Mulder gets out of the car, it's dark outside, but when the helicopter comes, it is still daylight. (00:25:00)
Continuity mistake: When Mulder is at Ground Control and the woman is telling the space ship that they're going into fly-by-wire mode, the Mulder's visitor pass changes from beneath his jacket to above his jacket between shots. (00:20:00)
Other mistake: When Doggett starts clawing at the freshly plastered wall, he does so at just below his eye-level and blood starts pouring from the hole he makes. The dead woman inside the wall was stabbed in the lower abdomen; there's no way that blood from the abdominal wound would've seeped through the wall at the level he was digging.
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.
Plot hole: When Mulder and Scully are going to the town/city where the disappearances took place Scully says they should stop so she can walk the dog. Mulder says OK because he has to ask for directions yet the next scene we see is Mulder and Scully interviewing Dr. Faraday. How did they find him if they didn't know where they were?. And after that we see them at a store where they do ask for directions. (00:08:30)
Continuity mistake: When Max bleeds out his ear, the blood stain on the pillow changes when Mulder and Scully see it. (00:32:10)
