The "practice" of embedding "evil" messages in songs, by recording them
backwards - somehow we were supposed to receive subliminal commands this way.
It comes from one of the Beatles little studio tricks of recording parts
backwards, as a means of inventing new textures. In the 70's, some Christian anti-rock crusaders used "Stairway to Heaven" ("Here's to my
sweet Satan") as "proof" that rock was evil; in the 80's, Judas Priest
were sued in a murder case for BM.