It looks like Microsoft is testing search ads that auto expand to reveal sitelinks under those ads within the Bing Search results. You don't need to click or do anything and the ad will dynamically expand to show more sitelinks underneath the search ad unit.
I spotted this while doing some testing, here is a GIF of it in action:
I am not a fan of things on a page expanding and pushing other things down on the page but hey, why not test it...
Forum discussion at X.
