During the last scene, Mulder's left hand and Marty Glenn's right hand change places on the bars between shots.
When Marty is on the street asking for directions, tall snow-capped mountains can be seen in the background. Delaware has no such mountains.
A Canadian-spec no stopping sign (black octagon inside circle) is visible in one shot.
The story takes place in Delaware, and the detective states in an early scene that he has "48 hours to convince the DA" to prosecute the woman. There is no "DA" in Delaware; all criminal cases are prosecuted by the Attorney General's Office.
At 20 minutes following the exam, Mulder says Marty's pupils dilated from some stimuli. Her pupils were already dilated (wide) during the exam, but contracted (got small) when she saw through the killer's eyes.
(Around 16 minutes) Scully says "Maybe it's more simpler than that." Simpler means more simple so she should have said either "Maybe it's more simple than that" or "Maybe it's simpler than that."