The Rolling Stones jumped far outside of their normal blues-rock comfort zone with 1967's 'Their Satanic Majesties Request' album, which featured ornate psychedelic influences, a trippy lenticular album cover, some of their most unconventional songwriting, and yes, a mysterious-sounding hidden track.

Many people accused the Stones of copying the template set by the Beatles' 'Sgt. Pepper's Lonely Hearts Club Band' album with 'Majesties.' In truth the Stones' work was characteristically darker and hazier, but it does seem possible they picked up this particular tip from their peers. Unlike the Fab Four, the Stones stuck their hidden number, 'Cosmic Christmas,' at the end of side one and didn't set it so it tortured dogs or played for all eternity.