Director Tun-Fei Mou paid a lot of attention to the film's historical accuracy and sought to create something that very earnestly captured his true-life source material doing years of research. He chose actors who purposely resembled Japanese people of the war era and even cast Korean kids living in China to play the Youth Corp as Mou thought Koreans most resembled Japanese kids of that era. Mou filmed the movie in Harbin, Manchuria where 731 was stationed. He used 731's real headquarters as a location, it was a school at the time of the shoot. When Mou took down the school's name and put the Japanese flag back, it horrified the local elderly who had lived through the war. One particularly upset old lady approached Mou and his crew and said "I knew they'd be back (the Japanese), I just hoped it wouldn't be this soon!"
There was no special effects industry in China when this film was made so many of the special effects in the film were done with real cadavers which director Tun-Fei Mou was able to obtain through connections of his. The frostbite experiment victim's arms were real corpse arms and the child's body was a real cadaver. Mou waited for a whole month to find a body the same size as the child playing the role. He was almost ready to give up when the local police called him telling him that a child had been killed in an accident. He got permission from the parents and filmed the child's autopsy, dressing the coroners up like WWII-era Japanese doctors. The close ups of the child's organs being removed were done by dissecting a pig.
The film's budget was only around $200,000, very low for a film of this scope and subject material. Tun-Fei Mou used a variety of cost-saving techniques to get an impressive, gripping film for little money. The gore was done mostly with real body parts both human and animal lending it a spectacular sense of grotesque realism. The vast majority of the actors and crew were Northern Chinese locals who were paid little. The People's Liberation Army also lent the production their support and most of the military equipment in film belonged to the Chinese army. Many of the Japanese soldier extras in the larger scene were Chinese army recruits.
The young woman who is subjected to the lengthy and torturous experiment involving frostbite is actually director Mou's niece. She was the only person he could find willing to play the disturbing and physically demanding role which involved holding a pair of real corpse arms which were frozen for real in the subzero Manchurian temperatures.She nearly contacted frostbite herself filming it.
Though many of the film's gore scenes involve use of real corpses or animal parts, the film's much controversial "cat scene" was supposedly a well done special effect. Tun-Fei Mou covered the cat with red-dyed honey which was licked off the cat by the rats. The cat survived, was cleaned up, rewarded with fish and sent back to his owner. One can notice if watching closely that the rats never bite the cat and it never stops moving or goes limp. The rats were caught by the local schoolchildren and were however set on fire near the end of the shoot which appears on film. The local farmers were apparently quite pleased with Mou for having done so. This statement by the director has been disputed by the crew members who worked on the film, claiming that he actually killed the cat and made up the story of the cat being unharmed to stave off controversy.