Nick Chinlund made a point of staying in character during the shooting of the episode, something which unnerved a lot of the cast and crew. Gillian Anderson in particular was quite affected as she had forgotten how intense an actor Chinlund was in the intervening five years. The only one that Chinlund dropped his persona around was David Duchovny who he would shoot hoops with during breaks in filming.
Donald Addie Pfaster was previously in season 2's Irresistible (1995) making him the third X-Files monster-of-the-week to appear in two episodes. First was Eugene Victor Tooms (season 1's Squeeze (1993) and Tooms (1994)) and the second was Robert Patrick Modell (season 3's Pusher (1996) and season 5's Kitsunegari (1998)).
An "orison" is a prayer.
Lyle Lovett was approached about recording a new version of "Don't Look Any Further" but his schedule wouldn't permit it. John Hiatt ultimately did the honors.