Here's an odd music thing.
Steve Reich wrote a piece called "clapping music" where two people clap and one person's rhythm goes slightly ahead and eventually circles back to be in sync again. This is how it works, done on a computer -- watch for 30 seconds but then stop if you're bored:
http://www.youtube.com/watch?v=eu-tRXgOrdg It can be done in real life too. You can watch this for maybe 30 seconds but don't watch the whole thing because it's not the cool part yet. (I skip the first 10 filler seconds in the link):
http://www.youtube.com/watch?v=BhhIZscEE_g#t=10s So now someone has taken this idea and some old movie footage and made their own version of it. Watch this for at least a minute, though I watched more:
http://www.youtube.com/watch?v=BY4bL_bO8sA Pretty clever.
(I looked into this based on a post on the Stranger's blog.)