By the late 1960s, we had turned from singles to albums, on which the sequences in which the songs were presented became as important and magical as the tunes themselves.

Sometimes, there would be something extra. A track not listed on the album cover, a surprise extra at the end, or something added to the mix after the album cover had been printed.

The Beatles started this phenomenon, with hidden tracks on two of their albums. The Who did it too,  as did The Clash, The Rembrandts, and Lauryn Hill, who scored a Grammy nomination with a hidden track.

And then there was back-masking, in which bands allegedly added mischievous, devious, or Satanic messages into their songs, which could be decoded by playing the records backwards.

Which Queen song, played backwards, says “it’s fun to smoke marijuana”? How did a song about the Queen become a surprise ending to the Abbey Road album?

And is there a hidden track in this episode of the Time Tunnel?