The Beatles were the first to popularise backmasking, a technique in which backwards sound is added to tracks that are designed to be played forwards. The Beatles originally used the process to hide humourous messages in their songs, a trend followed by a number of popular artists since.
Backmasking has been a controversial topic in the past, with some Christian groups claiming that it has been used to hide subliminal Satanic messages. This has led to anti-backmasking legislation being proposed, record-burning protests being held, and countless hours being spent by adolescents rewinding their tape decks and record players.
These days, backmasking is mainly used to hide little Easter Eggs in songs, often with a reference to other works, or for comedic effect. Of course, there's also some hidden messages that are so bizarre, not even the original artists have managed to explain them properly.
This list takes a look at twenty popular songs that have very creepy back-masked messages hidden in them, from heavy metal legends to pop chart toppers.