Not really a song, Thing-Fish's "Prologue" consists of a monologue by the main character, accompanied by a guitar/drums/bass instrumental piece. As an introduction to the play/album, Thing-Fish explains the origins of the Mammy Nuns: the Evil Prince was looking for a "plot fo de systematic genocidal remove'lance of all unwanted highly rhythmic individj'lls an' sissy-boys" -- that is: a way to eliminate black people and gay men. With assistance from the government, he was able to test his potion in a prison. The results were unexpected: administered in the inmates' mashed potatoes, the potion turned most of them into ugly creatures with a "head like a potato... lips like a duck." The experiment itself hints at the theory that the spread of AIDS in the U.S. was the result of governmental manipulations, something Zappa was tempted to believe.
The music backing the track is a typical 1980s Zappa guitar riff: heavy, crunchy, linear, very similar to "Ya Hozna" (on Them or Us) and "The Mammy Nuns," the piece following "Prologue" on the 1984 album Thing-Fish.