Writer Frank Spotnitz has claimed that his 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 . " 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
Unit 731
Unit 731
731 (The X-Files)