One more quick post for today...
Boing Boing has an interesting auditory illusion presented in the video clip below called the Shepard Scale.
"From Wikipedia: A Shepard tone, named after Roger Shepard, is a sound consisting of a superposition of sine waves separated by octaves. When played with the base pitch of the tone moving upwards or downwards, it is referred to as the Shepard scale. This creates the auditory illusion of a tone that continually ascends or descends in pitch, yet which ultimately seems to get no higher or lower."
So if you play the clip again and again and again, you'll get the illusion that it keeps rising in pitch when in fact, it does not!