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.
The newspaper article found by Scully states that Howard Graves' middle name is Thomas, yet on his grave his middle name is Patrick.
When Mulder and Scully are questioning Lauren in the investigation room, the piece of paper on Mulder's jacket changes place in between shots.
When the cup falls over when Lauren wants to see Mr. Dorlund, the box of tissues disappears in the last shot.
When Mulder breathes on the glasses to reveal the fingerprints, they show up as black. Unless Mulder's mouth is full of fingerprint powder, the fingerprints should have been white.
The pathologist states of the initial two victims that the esophagus, larynx and hyoid bones have been crushed like chalk, then immediately says that there's no evidence of tissue damage, despite having just described significant tissue damage.
When the doctor pulls the sheet down from the first body in the morgue, one of the victims' underwear can clearly be seen. While in the morgue, victim's bodies are stored unclothed so a full and complete autopsy can be completed. Leaving a victim's underwear on during an autopsy can hide potential evidence or injury.
The corpses in the morgue scene could be seen breathing. The chest of the one closest to the screen was seen moving.
Very obvious stunt doubles of Fox and Dana during the crash scene.
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.
When Lauren pulls into the parking lot at the office, a Canadian-spec "Do not enter" traffic sign (red circle with white rectangle inside) is visible in the background.
When they visit the Graves' tombs at the cemetery, Scully makes a comment that Sarah Lynn Graves, Howard's daughter, was "only three years old". Actually the dates on the stone say September 8th 1966 - August 3rd 1969. While the years indicate a three year period, Sarah died one month before her birthday, and thus would have officially 2 years. However, this may have been a deliberate simplification on Scully's part.