This took me a second to figure out what they were doing, but when I finally understood it, I went “Holy crap:”
I don’t pretend to understand the black geometric magic behind this trick, and I realize that knowing how to do this will save me from neither zombies nor North Korean missiles, but it’s a pretty darn cool trick for the bar.
Via Kottke
http://www.core77.com/posts/71650/This-Wonderful-GIF-Shows-You-How-to-Create-a-Perfect-Ellipse-by-Repeatedly-Folding-a-Circular-Piece-of-Paper