Total on-screen body count is 300+, making this the most violent Japanese movie to date.

The baby could not be filmed on location with the actors due to insurance regulations, so a real baby was filmed in post and matted in digitally in close-ups.

The forest locations, in near Mt. Chokai in Akita Prefecture, were inaccessible by road, and so all the equipment needed - including two imported Panavision cameras - had to be carried in by hand, a thirty-minute trek each way.

Because of the density of the trees, moving the camera with a crane was impossible. To get around this, the crew slung wires between trees and remote-controlled the camera across them, much like a cable car.

Neither Tadanobu Asano nor Daisuke Ryû used stunt doubles.

The bridge-burning at the end of the film had to be shot three times, twice in long shot and once in close-up. To allow the bridge to be re-lit, it was wrapped in thick fabric from top to bottom.

Some elements of the musical score were create with scrap metal.

Chinese opera choreographer Zhang Chun Xiang arranged the fight scenes.