Compact discs work through a
laser reading the pits burnt into the CD. This is great in that it's a cheap way to stick 630 MB or 74 minutes of music onto a cheap piece of
plastic, but bad in that any disturbance to the laser or any markings on the CD result in lost
data. Most CD readers nowadays have a
cache to store music while the laser is unable to read, but dealing with dirty or scratched disks is much harder. Sometimes, the reader simply tries to reread the damaged area, creating a continual
skip or even a high-pitched drone.
While this is a sign that something's wrong with the compact disk (dirt or damage), it's also a source of fun if you're lucky. If it pauses on
an interesting lyric, you too can enjoy having your stereo belt out rude words until someone stumbles over and shuts it off. Depending on the album and the type of skip, it can even be hard to tell if it's skipping. Some rock song climaxes are hard to distinguish from a three second loop. Minimalistic techno is especially bad that way, and I once enjoyed several minutes of Kruder and Dorfmeister before realizing it had been skipping by a random number of seconds, creating the illusion of a artist-driven loop. I imagine making a song that deliberately sounded like it was skipping would be a good way to annoy your listeners, but I haven't found it done yet, though I'm sure someone has.