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)
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.
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)
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)
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.
Continuity mistake: When Max bleeds out his ear, the blood stain on the pillow changes when Mulder and Scully see it. (00:32:10)
Via Negativa - S8-E7
Continuity mistake: At The Beginning of the scene, there is only what seems to be a remote control on the left-hand side of the TV. Five seconds later, a couple of VHS tape cases appear where the remote control was before. (00:08:46)
Continuity mistake: Although the subtitle states 08:02 PM at the morgue, the clock in the room shows 08:40. (00:12:40)
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)
Continuity mistake: When they find the cocoon, the body inside is completely different in appearance from one shot to the next shot of it.
Continuity mistake: When Mulder and Scully are arguing outside the hospital, after meeting Billy and Peggy, there is a woman in a red coat, behind Scully, who gets out of her car and then vanishes between shots. (00:19:30)
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)
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: 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)
