Only a few assets from "Resident Evil 1.5" could be recycled, as the principal locations in the final build were made to look more extravagant and artistic, based on photographs taken of the interiors of Western-style buildings in Japanese cities. These environments were created with a software program called SGI O2, and each background took two to three weeks to render. The maximum number of zombies displayed on the screen at one time was limited to seven, making it possible to use 450 polygons for the comparatively detailed models of Leon and Claire. The protagonists, instead of being given visible wounds, were made to limp slowly upon receiving heavy damage. Apart from the graphics, one of the most important new features was the "Zapping System", which was partly inspired by "Back to the Future Part II", a time travel-themed film sequel that offers a different perspective on the story of the original film. The voice-overs by the all-Canadian cast of "Resident Evil 2" were recorded before the actual cutscenes were completed, with each of the actors selected from a roster of ten people per role. Thereafter, the full-motion videos (FMVs) were created by filming stop-motion animations of action figures, which were then rendered to completed pictures with computer graphics (CG) tools. Ada's movie model could not be finished in time. Thus, she is the only main character not to appear in a pre-rendered cutscene.