high-end programs mainly used for 3D computer graphics, while co-producer and former animation director Eric Stough notes that PowerAnimator was initially chosen because its features helped animators retain the show's "homemade" look. PowerAnimator was also used for making some of the show's visual effects, which are now created using Motion, a newer graphics program created by Apple, Inc. for their Mac OS X operating system. The show's visual quality has improved in recent seasons, though several other techniques are used to intentionally preserve the cheap cutout animation look. A few episodes feature sections of live-action footage, while others have incorporated other styles of animation. Portions of the season eight (2004) premiere "Good Times with Weapons" are done in anime style, while the season 10 episode "Make Love, Not Warcraft" is done partly in machinima. The season 12 episode "Major Boobage", a homage to the 1981 animated film Heavy Metal, implements scenes accomplished with rotoscoping. Voice cast Parker and Stone voice most of the male South Park characters. Mary Kay Bergman voiced the majority of the female characters until her death in November 1999. Mona Marshall and Eliza Schneider succeeded Bergman, with Schneider leaving the show after its seventh season (2003). She was replaced by April Stewart, who, along with Marshall, continues to voice most of the female characters. Bergman was originally listed in the credits under the alias Shannen Cassidy to protect her reputation as the voice of several Disney and other kid-friendly characters. Stewart was originally credited under the name Gracie Lazar, while Schneider was sometimes credited under her rock opera performance pseudonym Blue Girl. Other voice actors and members of South Park's production staff have voiced minor characters for various episodes, while a few staff members voice recurring characters. Supervising producer Jennifer Howell voices student Bebe Stevens; co-producer and storyboard artist Adrien Beard voices Tolkien Black, who was the school's only African-American student until the introduction of Nichole in "Cartman Finds Love"; writing consultant Vernon Chatman voices an anthropomorphic towel named Towelie; and production supervisor John Hansen voices Mr. Slave, the former gay lover of Mr. Garrison. Throughout the show's run, the voices for toddler and kindergarten characters have been provided by various small children of the show's production staff. When voicing child characters, the voice actors speak within their normal vocal range while adding a childlike inflection. The recorded audio is then edited with Pro Tools, and