Google is testing a picture-in-picture mode for videos that are shown in the search results. You can click on the video preview image and play the video at the bottom right corner of the search results page.
This was spotted by Khushal Bherwani and he posted a video of this in action on Twitter. Here is a GIF of that:
I personally cannot replicate this, can you?
I am also not sure if I like this or not.
Forum discussion at Twitter.