Factual error: Mulder sees water going down the drain counterclockwise and says something is up since all water in the northern hemisphere drains clockwise. This is not true. Water can drain in both directions in both hemispheres. Things like convection currents, basin design, and residual swirl from filling the sink have a much greater influence. You would have to drain a small ocean to see the Coriolis effect, or use specially-designed test apparatus. See http://www.snopes.com/science/coriolis.htm and http://www.physics.ohio-state.edu/~dvandom/Edu/newcor.html (scroll down to *5.2. Water Going The Wrong Way Down The Sink* near the bottom of the page).
Continuity mistake: After the meeting with Dr. Davey, we cut to Mulder sitting in the train station trying to figure out what Dr. Banton was doing in the video. We see an overhead shot of the station, which shows a column in the far distance. Watch carefully: the shot never loses sight of the column, and you can see random passersby walk towards the column, but NO Scully. As the camera moves downwards to focus on Mulder in the foreground, Scully suddenly appears from behind the column, as if she had been walking towards it all this while. Obviously, she had been standing behind the column until her cue to come out.
Factual error: Mulder mentions the USS Eldridge as disappearing from Philadelphia (and later reappearing in Norfolk) "nine months after Roswell", i.e., May 1948. In fact, the supposed incident took place much earlier - in February 1943, according to almost all reliable sources.
Factual error: Scully reads to Mulder from a book all about flukes (Trematodes). However, the information she is quoting is wrong. She states that flukes or flatworms have a "scolex" with hooks and suckers. These are actually the distinguishing characteristic of cestodes (tapeworms). Trematodes have no scolex and definitely no hooks.
Other mistake: Unlike Mr Chaco, who has the brace clamped around his neck, Scully is clamped around the top of her head, which is a quite irrational way of executing a person, because the clamp does not serve as a stabilizer. In fact, in this arrangement, Scully is not fixed to the stand at all.
Visible crew/equipment: When Mulder and Scully are talking to the owner of the trailer park and he is berating Mulder, you can see the edge of the lens in the upper left corner of one shot. This is because the lens used was of a wide angle almost fish-eye type and the edge of the lens itself can occasionally creep into the frame on most cameras.
Revealing mistake: The answering machine at the end appears to not be plugged into any phone line. The shot shows the phone jacks on the right side of the machine are empty. In order for an answering machine to work at least one of those ports would need to be hooked to the phone.
Factual error: In the opening sequence, we see a nuclear attack submarine beneath the ice in the Arctic Ocean. When the captain orders the ship to surface, one of the crewmen mutters, "Surface to what? We're under 32 feet of glacial ice!" Except that they're not under "glacial ice," they're under Arctic sea ice, which ranges from about 6 feet thick in the summer to about 15 feet thick in the winter.
Add timeCharles Austin Miller
Continuity mistake: When Mulder is talking to Dana's mom about finding her cross (necklace) in the trunk, Scully's mom says that she gave it to her on her 15th birthday, but in Season 5 in Christmas Carol, Scully has a flashback to receiving it at Christmas.
Character mistake: Mulder asks Scully about "the fourth commandment about obeying the Sabbath, the part when God made heaven and Earth " However, Scully as a Catholic should know that this is the third commandment for Catholics. This is also an indirect indication that Mulder was raised in Jewish religion.
Plot hole: At his arrival at the Arecibo observatory, Mulder crushes the padlock on the door leading to the control building, and then he finds the native man, Jorge, in the toilet, who hid himself in the building. There's no way Jorge could enter the building and also lock himself in there with the padlock.