Revealing mistake: The guy who is jumping to the water is definitely not Mulder. It is a stunt. (00:21:20)
Revealing mistake: At the very beginning of the scene when the bomb is shown, in the lower part of the screen a moving red spot appears which probably comes from the reflection of the bomb's red diode in the camera. (00:36:50)
Revealing mistake: When Mulder finds the Japanese doctor dead on the floor of the train bathroom, the man's eyes are open. Just before the shot cuts to the girl and boy at the door, he closes his eyes.
Revealing mistake: In The Beginning of the episode two frogmen jump into the water from the boat. The boat is supposedly out in the Pacific Ocean, but in the lower left corner you can see a harbor in the background.
Hell Money - S3-E19
Revealing mistake: Mulder and Scully are standing behind the torso of a corpse being investigated. Despite being dead, the victim is breathing. (00:17:20)
Revealing mistake: As Dana Scully is examining the dead woman found in bed with Skinner, she observes a strange luminescent glow on the woman's nose and lips. It's apparent that this glow was added digitally; but the digital effect is "drifting" around the dead woman's face, seemingly out of sync with the video. Similar "drifting" digital effect problems are seen in other X-Files episodes.
Revealing mistake: In the opening sequence, a man who is hallucinating badly is apprehended by the police. They find a dead blonde woman in the trunk of the man's car. In a close-up of the dead woman, all the dried blood on her face is an added digital effect; however, the dried blood "drifts" around, seemingly out-of-sync with the video. Similar "drifting" digital effect problems are seen in other X-Files episodes.
Sanguinarium - S4-E6
Revealing mistake: When Mulder and Scully enter the doctor's house, you can see over their shoulders that it is showering with rain outside, yet both of them are bone dry.
Musings of a Cigarette-Smoking Man - S4-E7
Revealing mistake: As the smoking man sits on a bench after finding out his story was rewritten, there are mountains visible in the background. Atop one of the buildings in the background is a Canadian flag waving in the wind. This show was shot in Vancouver, but is set in Washington D.C. There are no tall mountains that close to D.C.

Unrequited - S4-E16
Revealing mistake: The handle and latch next to the supposedly working intercom on the chain-link security gate entrance to the "White Hand" facility is obviously non-functioning - when the gate is opened it can be seen there are no functional operating parts. (00:08:40 - 00:09:15)
Revealing mistake: The dead Mrs. Sim is supposed to be nude in the bathtub, but for a brief second, a glimpse of her head and shoulders reveals the very top of a flesh-coloured modesty wrap covering her breasts. This may not be visible in a non-widescreen format release.
Kitsunegari - S5-E8
Revealing mistake: When Scully pries open the mouth of the man who died from being forced to ingest paint, his eyes twitch. (00:13:50)
Schizogeny - S5-E9
Revealing mistake: A heavy rain is falling but there is no sign of it on Mulder and Scully. (00:32:00)
Revealing mistake: When the doctor examine Ronnie's "corpse" in the morgue, he pulls out the stake. It is quite obvious that he's struggling with a wooden stake that is placed on the actor's side, not through his chest. Moreover, the camera pans up and you can briefly see Ronnie's unharmed chest.
The Red and the Black (2) - S5-E14
Revealing mistake: It seems that in the first shot the doctor injects something into the vaccine vial rather than extracting from it since the syringe plunger is moving inwards instead of outwards. In the next shot one can see that the syringe is being filled with the vaccine, however the arrangement of doctor's fingers is suitable for injection, which strongly suggests that the scene is played backwards. (00:17:55)
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)
Revealing mistake: When Scully grabs Mulder's hand, his watch shows 11:25 AM, but when the agents enter the house, the scene's stamp reads "Phoenix, Arizona, 4:58 PM." (00:17:55)
Revealing mistake: When Mulder - whilst trapped in the body of Morris Fletcher - is doing various poses in front of the mirror, several of his movements and the corresponding movements from the realized reflection of Morris Fletcher are slightly out of sync with each other.
The Sixth Extinction (2) - S7-E1
Revealing mistake: When Scully enters the F.B.I. Building after returning from Africa, she isn't wearing her badge. She'd need it to walk around without being stopped by security. (00:35:50)
Chosen answer: Yes.
Tailkinker ★