it is a rewritten substitute. Meanwhile, the real journal is translated in a shadowy room as the Smoking Man watches. Production Conception and writing Writer Frank Spotnitz's inspiration for the episode came from having read an article in The New York Times on the war crimes committed by Unit 731 of the Imperial Japanese Army, after which the episode is named. The unit was responsible for human subject research on both prisoners of war and civilians. Further inspiration was drawn from the films North by Northwest and The Train, which were the basis for the episode's train-car setting. Spotnitz also noted that the episode offered the writers the opportunity to "set the counter back" for the series' premise, allowing the character of Scully to still maintain a skeptical standpoint after the events of "Paper Clip", an earlier third-season episode in which the character witnesses a group of aliens. The tagline for this episode was switched to "Apology is Policy." Filming and post-production The scene at the start of the episode with Duchovny's character Fox Mulder clinging to the side of the train car was filmed using a harness cabled across the top of the car that was removed digitally during post production. Duchovny performed the stunt himself, without the use of a double. Steven Williams and Duchovny separately recorded the scene in which Williams carries Duchovny from the car before it explodes against a blue screen. The results of this were flipped horizontally to aid the scene's "composition", and superimposed over the explosion. Twenty-five masked actors, mostly children, laid over prop bodies for the scene with the mass grave. The producers built train car interiors for the quarantine car where the patient was being kept and the sleeper cars, and floated the train sets on inner tubes to create the feeling of movement. Seven different cameras were used by director Rob Bowman when filming the train car explosion. Forty-five gallons of gasoline and 120 black-powder bombs were used for the effect. The car used had been obtained cheaply from Vancouver-based BC Rail, and had been considered scrap due to being bent. After the explosion was recorded, a bell from the train was recovered some distance from the site by the physical effects supervisor Dave Gauthier, who had it polished and engraved with a message for Bowman. Bowman made use of a Steadicam for those scenes that featured Mulder inside the