Steven Spielberg has acknowledged that he had to engage in a certain amount of maneuvering during the production of War Horse -- a movie set during World War I, which claimed more lives on the battlefield than any in history -- to retain a PG-13 rating. In an interview with Daily Variety , Spielberg said that while directing the movie he was "always" conscious of the difficulty of pulling that strategy off. "That's why there's hardly any blood at all in War Horse ," he noted. Spielberg said that until he began work on the movie, he was unaware that millions of horses used by the military on each side were killed during the four-year conflict -- "not just by the wounds of war but by neglect and disease and exposure and malnutrition" as machines took over their role in warfare. But, to obtain the PG-13 rating, the Battles involving them were reduced to only about 10 minutes in his movie, Spielberg observed, as he decided to focus on the "connections between characters" instead.