I've heard from quite a few people that Twirl Girl has created significant physical and mental discomfort. But just in case you've finally mastered that particular mindbanger, here's another:
If you can't figure out what's going on, check the file name.
EDIT: Lest I incur the wrath of math geeks, I retract my hint. It's not a fractal.
If a thing which contains infinite nested repetitions of itself isn't a fractal, what is it? Or is it that it isn't a fractal because it's technically just a loop that makes us think it contains infinite nested repetitions of itself?
check this link out...
http://www.post-literate.com/gerpunx/archives/2005/01/prepare_to_lose_your_mind.php