BACKMASKING       

     One of my friend told me about backmasking. Backmasking (also known as backward masking) is a recording technique in which a sound or message is recorded backward on to a track that is meant to be played forward. Backmasking is a deliberate process, whereas a message found through phonetic reversal may be unintentional. ________________________________________________________________________________

Here are some example of backmasked songs

http://www.youtube.com/watch?v=_UVDlg4x468