Development of "Cortex Strikes Back" began in October 1996. For the game, Andy Gavin created a new engine and scripting language named "Game Oriented Object LISP 2" (GOOL 2) that was three times faster than the previous game's engine, could handle ten times the animation frames and twice the polygon count. The jungle levels were originally to have featured ground fog, but this was abandoned when magazines and the public began to heavily criticize other developers for using fog to hide polygon count. Sunlight and depth accentuation was experimented with for these levels. Wanting to have some "dirty" locations in the game, Naughty Dog worked in the sewer levels and added color contrast to the levels to show depth and break up the repetitive monotony of the endless sewer pipes. A flat plane z-buffer was created for the game; because the water surfaces and mud in the jungle had to be a flat plane and be exactly flat on the Y-axis, there could be no waves and the subdividing plane could not be at an odd angle. The effect only worked on objects in the foreground and was only used on Crash, some enemies and a few boxes at the same time. The soundtrack of "Crash Bandicoot 2: Cortex Strikes Back" was provided by Mutato Muzika (consisting of Mark Mothersbaugh and Josh Mancell), while the sound effects were created by Universal Sound Studios (consisting of Mike Gollom, Ron Horwitz and Kevin Spears). The characters were designed by Charles Zembillas of American Exitus, Incorporated. Clancy Brown provided the voice of Doctor Neo Cortex, while Brendan O'Brien voiced the dual role of Doctor N. Gin and Doctor Nitrus Brio and Vicki Winters voiced Coco Bandicoot. The game was unveiled at the Electronic Entertainment Expo in Atlanta, Georgia in June 1997 to a positive response from the game industry. The game went into the alpha stage in August 1997. Around that time, Dan Arey, the lead designer of "", joined Naughty Dog and streamlined the level design.