 Chad Donella was cast as the lead monster because he possessed a " subtle , interesting quality , " according to casting director Rick Millikan . Director Kim Manners latter described Donella as a " great little actor . " Duchovny 's stunt double , Steve Kiziak played the role of the private detective — also called Steve Kiziak — that Roberts kills and eats . Kiziak later said , " It was a lot of fun to be in front of the camera . " Kiziak had first appeared as Duchovny 's body double in the third season episode " 2Shy , " and would later appear as a Mulder lookalike in " Fight Club . " 
