There's a whole pseudo-science behind this "backward masking."
Some claim it's malarkey because everyone would put in subliminal
messages to sell more CDs and such.
There are some scientists, however, who believe that the subconscious
reveals itself through messages played backwards.
http://www.reversespeech.com/Simple_Examples.htm
They are not admissible in court, though some psychologists
believe that reverse speech can be used as a confession.