Visible crew/equipment: I don't know if this is visible in all formats, but on the newest UK release on DVD, watching in widescreen, it's amazingly obvious. When Mulder recovers from the vampire attack, he gets up from the floor and breaks up a chair to make a stake. There is a shot of his feet as he smashes the legs off and bends to pick up a piece. In the bottom left hand corner of the screen, you can see a crew member's hand carefully and quickly placing a piece of wood on top of the pile for Mulder to pick up.
Factual error: Early in the show, 3 Marine officers are being questioned about the death of a 4th. All 3 are wearing the Marine insignia on their jacket lapels reversed. [The anchors should point IN, not out] That mistake is corrected for some characters later in the episode, however at least two of the officers are seen later without their jackets, and their shirts do not have military creases - 2 in the front, 3 in the back - standard for a Marine blouse.