Google is testing showing expandable video previews in the search results. When you hover your mouse over a video thumbnail in the Google search results, the video will expand and play a silent preview.
This was spotted by Brodie Clark who posted this screen capture of it Twitter:
The test does not surprise me - Google has been making videos slowly and slowly more engaging in Google Search for years.
Brodie said "A test where YouTube video content is more engaging in Google's search results. Hovering over a video starts the preview on desktop (normal), with the video then becoming larger + including the description (test)."
Forum discussion at Twitter.