Continuity: The first time Scully walks into Mulder's office, we see his "I want to Believe" poster in full view. Later on in the scene, we see papers stacked in front of it.

Continuity: When Scully goes to Mulder's room, thinking she has the marks, after he has checked her we see Scully's hair is behind her collar, but when the shot changes to her going to sit down, her hair is now hanging out.

Continuity: When we first see Scully, going into the office at the beginning of the episode, we see when she is on her way to the office and when she enters it she is wearing her badge, yet when the shot changes, it is no longer on her, then when she comes out she is wearing it again.

Continuity: When Scully is in her room after the autopsy, we see the x-ray attached to her lamp. When we first see it, we can see the letters LD on it, yet when the shot changes back to the x-ray after Mulder has gone, we can only see I, presumably the other x-ray is now overlapping it.

Continuity: When Mulder and Scully are driving after their plane lands, we see at one point that Mulder has his left hand on the wheel and he is eating a sunflower seed with his right, yet when the shot changes he's driving with his right hand and eating with his left.

Continuity: When Scully is having lunch with her friend just after the intro, we see at one shot from behind her she is holding a knife, then when the shot changes she is no longer holding it.

Continuity: When Tooms is in the cell right at the end, we see when his food is being brought over to him on the tray that there is a drink and a bun, when the shot changes to the other side of the door the drink and bun have swapped sides. When the shot changes back to the other side of the door, the tray is now the other way around and then when the shot goes back to the other side the whole tray has now disappeared.

Factual error: Scully tells Mulder that Ruby is alive, so why is she performing CPR on her?

Continuity: When Mulder is running after the boy near the end, and the motorcycles are coming, we see him throw the torch quite far away, yet when the motorcycles are gone we see it is right next to him.

Factual error: Atlantic City, New Jersey really doesn't have woods around it like it does in this episode.

Visible crew/equipment: When Mulder and Scully are talking about Howard Graves faking his own death, when they get to the bottom of the stairs, you can see the pole which the camera used to travel down the stairs.

Continuity: Howard Graves' tombstone states that he died on the 5th of October, but the opening scenes date stamp says the 22nd of September when it was supposed to be two weeks after Graves had died.

Continuity: When Mulder and Scully are questioning Lauren in the investigation room, the piece of paper on Mulder's jacket changes place in between shots.

Continuity: When Mulder and Scully are leaving Laurens house, when we see the doors lock themselves they are different locks to what the car actually has.

Continuity: When the cup falls over when Lauren wants to see Mr. Dorlund, the box of tissues disappears in the last shot.

Revealing: While the computer is being infected with the virus, Peterson turns away from the screen to face Scully. Two seconds later, after the shot of Scully, the same shot is shown again but in reverse so that Peterson turns back to the screen. It's more obvious if you look at the weird way his eyes blink in the reversed shot.

Audio problem: When Jerry uses the elevator, the voice of the computer reads out the floors as "twenty-third floor, fourth floor, fifth floor" etc, missing out the "twenty-" prefix until the 29th floor. The DVD subtitles list these numbers with their prefix, so this was not intentional.

Continuity: When Brad is showing Mulder and Scully the video tape in his house, you can see the crew reflected off the TV screen.

Continuity: At the beginning when a man says: "We're not who we are", he says it differently when Scully watches the tape.

Plot hole: The worm is supposed to increase production of a violent hormone, making the host incredibly violent and unable to control it. Yet the infected member of the group manages to hide it perfectly between making their first kill and being discovered by the rest.