backmasking(Backmasking is a recording technique in which a message is recorded backward onto a track that is meant to be played forward. It is a deliberate process, whereas a message found through phonetic reversal may be unintentional.
Artists have used backmasking for artistic, comedic and satiric effect, on both analogue and digital recordings. It has also been used to censor words or phrases for "clean" releases of explicit songs.
In 1969, rumors of a backmasked message in the Beatles song "Revolution 9" fueled the Paul is dead urban legend. wikipedia.orgAlexander Demidov)
