It's Just An Illusion (Ooh Ooh Ahh Ahh!)

Here's quite a cool little auditory illusion (as opposed to the visual kind). It is called the Shepard-Risset glissando, and it sounds like continuously rising scale. In fact it really does not go anywhere since the first note is the same as the last, but the differing volumes of the notes in the scale give that strange sensation that you are continually ascending.

Listen to it here: Shepard-Risset glissando

More information, and an explanation of the pictorial representation, on Wikipedia. Now, what I'd like to see is this as a kind of warm up for the choir!