Keith Chan has found AdSense toggle ads(see the sreenshot on the right). What looks. it might be an experimental form of Google AdSense. In the screenshot, there are two blue arrow icons at the bottom left of the text ad unit. Clicking the down arrow scrolls into view a couple of new ads. He has also made a video showing this in action. Watch the video after the jump.
Google, AdSense, AdSense Ads, Toggle Ads, Scrolling Ads, Internet Video