But it was in the 1990s that hidden tracks became almost de rigeur, as more artists discovered that the young compact disc format made it easier to disguise an album’s contents. It’s harder to hide music on a vinyl record because the grooves are visible, but CDs, people soon found out, could conceal secrets.
Nirvana’s “Endless, Nameless,” at the end of Nevermind, became perhaps the most famous example. At first, the bonus song was hidden almost too well. Howie Weinberg, who was in charge of mastering the album after its recording, omitted the song accidentally. When Kurt Cobain found out, he was furious and so Weinberg immediately reinserted it, placing it after a 10-minute silence that followed the last titled track, “Something in the Way.”
via Wondering Sound.