Character mistake: When Josepho meets Agent Scully, he recites to her the passage from the Bible that begins with the phrase: "Behold, a whirlwind came out of the north" Then he asks her if she knew that fragment from the Bible. She answers: "Ephesians." Unfortunately, she is wrong, because this fragment comes from Ezekiel 1:4. (00:30:30)
Other mistake: While Cadet Hayes is being interrogated, he says, "I studied the photos of your son's death. They called to me. I don't know why, but it was a message and I listened." Then Scully answers, "And then you killed Agent Doggett's son." This answer is illogical and complete nonsense because the photos of Agent Doggett's son were taken after his death. (00:36:05)
Factual error: Dogget says that "It would require something 4,300 times the density of steel to cause this damage." Steel is about 8 times denser than human flesh, so bearing in mind that density is proportional to mass at constant volume, it means that Ray would be 4,300 x 8 = 34,400 times heavier than if he were a regular human being. Assuming that he normally weighed about 80 kg, after the transformation he would weigh 80 kg x 34,400 = 2,752 tons. It means that hardly any ground would support his incredibly huge mass, let alone items such as a bed, chair, stairs, building structures, etc.
Audio problem: Fellig is confronted by the murderer and you can hear the sound of a switchblade knife opening. When the knife is shown in Fellig's back and later in the evidence bag, however, it is a butterfly knife and not a switchblade.
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)
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)
Soft Light - S2-E23
Plot hole: If the shadow acts like a black hole and tears apart all atoms that enter it why does it only seem to affect people (but also their clothing and anything else on them)? Surely Dr Banton would be destroying everything around him.
Factual error: At The Beginning of the scene, XO Johanson is looking through the periscope. However, it is nonsense, because the submarine was in silent running, and the Japanese destroyer was circling it, so the sub must have cruised in deep submersion. The water depth there was approx. 270 meters, as the French salvage team claims at The Beginning of the episode. There is rarely any significant light beyond 200 meters. Looking through the periscope in these conditions would be completely useless. (00:32:25)
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)
Other mistake: Eve 6 says that ordinary human beings have 46 chromosomes, while the Adams and the Eves have 56 chromosomes. This makes 10 additional chromosomes. However, Eve 6 also mentions that they have additional chromosomes number 4, 5, 12, 16, and 22 - only 5 additional chromosomes. (00:22:40)
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)
Visible crew/equipment: After talking to the scientist about his car, Mulder and Scully are talking in front of a door. In the glass of the door is a reflection of a third person.
Continuity mistake: When they find the cocoon, the body inside is completely different in appearance from one shot to the next shot of it.
Visible crew/equipment: During the scene when Mulder, Scully and the deputy approach the farmhouse there is a moment when Scully walks up to a chicken coop and a boom microphone with a fluffy wind cover on can be seen coming up from the bottom of the screen (Underneath Scully). (00:30:35)
Deep Throat - S1-E2
Visible crew/equipment: When Mulder and Scully attempt to interview Col. Kissell, as he gets out of his car, you can see a square light reflector screen reflected on the car door. (00:12:37)
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)