In order to prepare for their roles, several cast members watched a number of real autopsies.
Most of the organs seen in the movie came from pigs and cows.
The city was identified as Philadelphia in an earlier draft of the script.
Due to disturbing behavior throughout - including violence, gruesome images, strong sexual content - the first theatrical trailer of the movie was digitally altered. It showed operation scenes without human organs, also Milo Ventimiglia's hands digitally erased in a love scene. But the later Red Band version was released without any alterations. See also Into the Blue (2005) and The Hangover (2009).