Many listeners are familiar with the idea of a "hidden track," generally a track on an album that isn't listed in the liner notes that plays at the end. Commonly it's an extra track at the end of a CD or the CD's last track will have a long gap of silence following by the song. Less common and less well known is the hidden "pregap" track--a track added to the beginning of a CD that can only be accessed by manually rewinding past the beginning of the first track. I found out about this reading about Kylie Minogue's Light Years, which has such a track called "Password." To access it, start playing "Spinning Around," push and hold the manual rewind, which will rewind past the beginning of the song and then start counting up. Around 3:48 "Password"begins. It only seems to work on CD players, not computers.
Other albums that have pregap tracks include Bloc Party's Silent Alarm ("Every Time is the Last Time") Ash's 1977 (there's two, "Jack Names the Planets" and "Don't Know"), and Blur's Think Tank. Here's a list from Wikipedia: