And to "ermergingmatt", "Ampara" and the other doubters - the animation does not change directions, it is an optical illusion. If you don't believe me, open up the GIF in a graphics editor and have a look, it is the one sequence of images (34 to be exact) cycling continuously. The illusion works because of the lack of depth cues - you can't tell whether she facing towards you or away, so your brain "picks" one direction and interprets the rest of the images appropriately.
Cool trick: open teh image in2 browser windows and have her cycle in both directions at once. Then, try to get them *both* to change directions. For added challenge, at the same time.
Note: I haven't succeeded with the simultaneous switch yet, but it's fun to try.