Six months of pre-production began in December 1979. Spielberg preferred to spend a year in pre-production, but worked at a faster pace to keep the budget low. Spielberg and Lucas were both simultaneously working on other projects. Artists Ed Verreaux, Dave Negron, Michael Lloyd, and Joe Johnston provided extensive storyboarding, with over 80% of the script represented, equalling approximately 6,000 images. This helped Spielberg pre-visualize scenes and limit the time taken to set up shots. The script only described the opening of the ark as "all hell breaks loose", and the artists were tasked with envisioning what should happen. Each offered different aspects: spirits, flames, and weird light effects; Johnston was tasked with combining all three. Spielberg also had miniature sets of larger scenes built to plan layouts and lighting, including the Well of Souls, the Tanis dig site, and the Cairo marketplace. They contained 1-inch tall figurines to suggest how many extras would be required. Among changes made at this stage, Spielberg abandoned his idea for Toht to have a mechanical arm that could be replaced with a machine gun or flamethrower. Lucas said it put the film into a different genre.