The team placed high priority on Mario's movement, and before levels were created, they tested and refined Mario's animations on a simple grid. The first test scenario for controls and physics involved Mario interacting with a golden rabbit, named "MIPS" after the Nintendo 64's MIPS architecture processors; the rabbit was included in the final version of the game. The developers tried to implement split-screen cooperative play using Mario and Luigi simultaneously where the two characters would start at separate points in the castle and work their way through the game together. The two-player mode was eliminated because the developers were unable to make the gameplay work satisfactorily. To assist players with depth perception, the team positioned a faux shadow directly beneath each object regardless of the area's lighting. Assistant director Yoshiaki Koizumi described the feature as an "iron-clad necessity" which "might not be realistic, but it's much easier to play." Miyamoto's guiding design philosophy was to include more details than earlier games, using the Nintendo 64's power to feature "all the emotions of the characters". He likened the game's style to a 3D interactive cartoon. Some details were inspired by the developers' personal lives; for example, the Boos are based on assistant director Takashi Tezuka's wife, who, as Miyamoto explained, "is very quiet normally, but one day she exploded, maddened by all the time Tezuka spent at work." In the game, the Boos shrink when Mario looks at them, but when he turns away, they grow large and menacing. "Super Mario 64" features more puzzles than earlier "Mario" games. It was developed simultaneously with "", but as "Ocarina of Time" was released more than two years later, some puzzles were taken for "Super Mario 64". Information about "Super Mario 64" was leaked in November 1995, and a playable version of the game was presented days later as part of the Nintendo 64 premiere (then known as the "Ultra 64") at Nintendo Space World. At this point, the basic controls had been implemented and the game was 50% finished, featuring 32 courses, though only about 2% of mapping was complete. Miyamoto had hoped to create more courses, but only 15 courses could fit. According to Nintendo of America chairman Howard Lincoln, Miyamoto's desire to add more to the game was a major factor in the decision to delay the Nintendo 64 release from Christmas 1995 to April 1996. Nintendo president Hiroshi Yamauchi later commented, "Game creators can finish games quickly if they compromise.