Backmasking is a technique of hiding messages in songs. I recently listened to the song "Jingle Bells" and felt it was scary when I heard the song in reverse. So scary that I shrieked and threw my headphones at the screen. Click here to listen to this.
This was the second most scary thing I have encountered in my life... The most scariest being seeing S.J.Suriya dancing to the song Mayil Iragaey... on Sun Music the first time.