Backmasking (also known as backward masking) is a recording technique in which a sound or message is recorded backward onto a track that is meant to be played forward. Backmasking is a deliberate process, whereas a message found through phonetic reversal may be unintentional.
Backmasking was popularized by The Beatles, who used backward vocals and instrumentation on their 1966 album Revolver. Artists have since used backmasking for artistic, comedic, and satiric effect, on both analog and digital recordings. The technique has also been used to censor words or phrases for "clean" releases of songs.
Backmasking has been a controversial topic in the United States since the 1980s, when allegations from Christian groups of its use for Satanic purposes were made against prominent rock musicians, leading to record-burning protests and proposed anti-backmasking legislation by state and federal governments. Whether backmasked messages exist is in debate, as is whether backmasking can be used subliminally to affect listeners.
Jeff Milner http://jeffmilner.com/backmasking.htm
Something else, that I found. This stuff has to be proven to me.
We've heard about "Stairway to Heaven": Play it backwards and you'll hear devilish sayings. Or so "they" said. Now, thanks to the miracles of Jeff Milner's backmasking, we've learned that it's true. But it doesn't stop with Led Zeppelin. Take a song as innocent as "Imagine" by John Lennon. Play the clip forward. John plaintively sings, "Imagine alllll the people." Then, reverse-play the excerpt. Lo and behold, he's actually saying "the people war against me"! Or how about the "Pokemon Rap"? Millions of children around the globe adore the rotund, golden fellow. How bad can he be? When played forward, the song chirps: "Gotta catch 'em all, gotta catch 'em all (yo)." But when exposed by reverse playing, the yellow beast is actually chanting: "I love satan, I love satan"! Jeff, without you we might have continued in total obliviousness. Rock on, buddy. http://picks.yahoo.com/picks/i/20060603.html