listen to this for a little bit and you should notice something weird.this is a REALLY simple audio illusion; its just three sine waves usually.
you can skip to about halfway if you want to hear it go down, but I don't know if its as good.
its not perfect and a better version can be found here:
http://www.youtube.com/watch?v=BzNzgsAE4F0
hypnotizing
wow