Factual error: A 747 jumbo jet is shown in the first scene of the episode. Later we can see the aircraft cabin with a 3X3 seat configuration. However, there is no 747 with such layout. (00:01:40)
Factual error: The date stamp says that it is April 12 and Scully says that it is Sunday, but April 12, 1997 was a Saturday. (00:03:10)
Factual error: When Scully is performing the autopsy on Leonard Betts' severed head, she states "As remains are incomplete, all observations refer to a decapitated head." This phrasing is redundant. The proper terminology would be "disembodied head." As a medical doctor, Scully should know this.
Unrequited - S4-E16
Factual error: By its uniforms, rank insignia (i.e. point-down chevrons), drill and instrumentation (e.g. tubas instead of sousaphones), the military band performing at the re-dedication ceremony at the Vietnam War memorial in Washington is a Commonwealth (probably Canadian) band and not an American band. Unlikely at a formal military ceremony in the United States.
Factual error: Gonzales shot himself in the forehead but he's got the back of his head intact - no exit wound. (00:27:40)
Factual error: In the background the full moon is visible and it's early morning (approx. 6:00 AM). However, at the start of the episode we see the full moon at night (approx. 19:50). Due to the fact that these are consecutive days, this situation is impossible from an astronomic point of view. (00:14:35)
Factual error: The last number on the truck's license plate is "77." On Russian plates the last two/three digits stand for a registration place. "77" is a number for Moscow, but the Gulag is located in Krasnoyarsk region, so the number should be different. Besides, the format of the plate (LDDDDL|DD) is incorrect - the correct one is LDDDLL|DD (L - letter, D - digit). (00:11:05)
Tunguska (1) - S4-E8
Factual error: This is probably the first time in history of civilized mankind that a person with a diplomatic visa is full-body-cavity searched, not to mention the illegal opening of the diplomatic bag. (00:04:05)
Factual error: The episode is supposed to take place in Traverse City, Michigan, United States. Mountains are visible in the sequence when Mulder is chasing after the killer on foot. The show was shot in Vancouver, British Columbia.
Musings of a Cigarette-Smoking Man - S4-E7
Factual error: In the US classified information system there is "compartmented information", but there's no "compartmentalised information." (00:08:00)
Never Again - S4-E13
Factual error: The first time we see Ed's tattoo, it is supposed to have been freshly done and he even removes the new bandage. However, there is no blood or excess ink on his arm, no redness around the lines, no swelling at all; no way at all that it could be a fresh tattoo.
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