Here is another test Google is trying in their search results. This one shows up in mobile image search where it seems to show the sticky header but also this “related images” hover over that when you click on it, takes you to different images.
This was spotted by Kapil Chadha on Twitter who captured this screen shot of it in action:
I honestly do not find this test to be that useful. I mean, it is super hard to see the images in the “related images” hover over feature. So I am not sure how useful the feature is if you cannot even see the images.
I do find the sticky header on mobile to be interesting, as we have only seen it thus far on desktop search.
Forum discussion at Twitter.