According to the CIA: Record yourself, play it backwards. Your darkest secrets are revealed.

In 1983, David Oates dropped his walkman into the toilet. If you're under 40 years old, a walkman was a portable cassette player. If you're under 30, a cassette was how we listened to music in the stone age. Anyway, after being dropped, David's tape player would only play tapes in reverse. At first, he found this entertaining. There were lots of songs that contained hidden messages that you could only hear if you played them backward. But *those* messages were placed there intentionally. Soon, David discovered messages hidden in human speech that were NOT intentional. Messages that were put there by the speaker's subconscious.