The animation looks like a genie-like animation, where you hover your mouse cursor over the ad and the ad does this genie-like animation.
One publisher posted an animated GIF of this in action. Here is that picture:
I've personally never seen this test, but Google seems to have been ramping up the AdSense user interface and style tests recently. The other day, we saw favicon images in AdSense ads again.
I wouldn't be surprised to see more of these reports in the near future.
Forum discussion at WebmasterWorld.