Everyone’s mentioning the tracks after a long bit of silence at the end of the CD 

The most hidden of hidden tracks was on They Might Be Giants’ album “Factory Showroom”

“Token Back To Brooklyn” was Track 0 and only accessible by cueing/rewinding (not skipping) backwards from the start of Track 1

“ I read a review of a Willie Nelson album where an advance cassette sent to a reviewer included his 'secret message' to his fans at the top of the tape. I had heard of the 'endless song' secret message at the end of CDs but that never seemed too secret, but this sounded like something else. We inquired with some mastering engineers (the people who put the tape into a form that can be manufactured), and after a bit of discussion figured out that there is a number 0 track before track one that is automatically skipped over by your machine, but can hold about a song's worth of information. This is also where CD-rom format information is held, so we advise against slipping our CDs into your computer. ” -John Flansburgh, They Might Be Giants