The most outrageous twist in the new R-rated South Park movie, Bigger, Longer & Uncut, which opened June 30, may not be that Saddam Hussein tries to make a manwich out of Satan, or that Winona Ryder appears to commit unspeakable acts with table-tennis equipment, or even that the filmmakers found a way to slip in a Jar Jar Binks joke. It’s that the last laugh really seems to be on the movie industry itself.

On screen, the Motion Picture Association of America becomes Public Enemy No. 1 when third graders Kenny, Kyle, Eric, and Stan sneak into an R-rated movie, learn loads of dirty words from the Canadian-made Asses of Fire, and, bada-bing bada-boom, America goes to war with Canada. Off screen, the battle zone was confined to California, where South Park creators Trey Parker, 29, and Matt Stone, 27, and exec producer Scott Rudin, 40, decided to test MPAA ratings guidelines as well as Paramount’s patience. ”After a while, we’d try to get anything we could past the MPAA,” says Stone outside the Santa Monica soundstage where he and Parker made the cuts on Uncut, ”and that really p—ed off Paramount.”

The behind-the-scenes brouhaha offers a rare peek into the secretive process by which filmmakers, studios, and the MPAA collaborate to rate a movie. Entertainment Weekly has obtained an 11-page interoffice memo, prepared for Rudin after talks between the MPAA and a Paramount exec. The transcripts of those conversations reveal just how arbitrary and open to negotiation the MPAA can be. With debate raging over the impact of movie violence and profanity on children and theaters pledging to ID ticket buyers at R-rated films, Uncut‘s full-frontal attack on the ratings system could turn the film into a lightning rod in the middle of the summer’s biggest cultural tempest.

South Park was screened by the MPAA six times. Five times, the board returned the movie to Paramount with an NC-17. Possible cuts were then hashed out between the board and the studio in the sort of negotiations usually reserved for signing a star quarterback. The transcript, dated March 24, reveals a smudged line separating R from NC-17. ”God f—ing me up the a– ” is grounds for an NC-17, but ”God’s the biggest bitch of them all” is perfectly R-rated. Say the word fisting and it’s an R; define that word on screen and nobody under 17 is admitted.

Throughout the intense, strangely humorless discussions, the Paramount exec pleads the studio’s case, telling the raters how hard it is to make changes in a cartoon, imploring them to watch the movie again and pointing out things they might have missed, often with unintended comic effect. ”The Ping-Pong balls are supposed to look like they’re coming from her vagina,” the exec says after concerns are raised about Ryder’s talented private parts, ”but she stands up and you know that it’s not. She’s holding a paddle.” The board seems satisfied. ”That helps,” one representative says.