Factual error: When Byers asks Langly to try under active cases to find Holly Modeski in the FBI database, Langly only presses two or three keys on a keyboard, which is obviously not enough to enter "Holly Modesky" to the search engine. (00:19:40)
Factual error: When two unidentified men who approached Susanne Modeski in the warehouse take out their handguns, they have regular pistols. However, when they start to shoot, continuous fire is heard that could only be produced by an automatic weapon. (00:28:40)
Suggested correction: Fully automatic pistols exist, such as the Glock 18.
Continuity mistake: When the Lone Gunmen speak with Susanne Modeski, in the background there are some cars parked in front of the Stadium Inn. However, just seconds after, when the telephone rings, there is a white truck parked at the entrance. Later on, the cars are back again. (00:38:55)
Visible crew/equipment: When the Lone Gunmen catch up with Suzanne at The End of the episode, when she is talking to them and the camera is on the three, you can see not one, but two boom mics at the top of the screen. (00:40:20)
Factual error: When Suzanne Modeski retreats to the restroom with a pair of pliers to pull out her tooth, she is only gone for approximately 15 seconds before the gunmen follow her. For a petite woman to rip out a strong, healthy molar from her own mouth (which also had metal prongs Underneath in her gum) would not take so little time, no matter how determined she was. It's also highly unlikely that the lack of anaesthetic would have allowed her to do so without making pained noises.
Continuity mistake: During the shootout in the warehouse, a wedding ring is visible on Mulder's finger. While it's possible Mulder was married before, the Lone Gunmen are shown hacking into Mulder's FBI dossier and Langly reads out that he is single.