Google is testing yet another Google+ integration in the search results. This one is named "Actively Discussed On Google+" and shows up for some users.
The feature basically gives you an additional link under the search results that says "Actively Discussed On Google+." When you click on the link, it will expand and show you the discussion happening in Google+.
I was able to replicate it when using Chrome on my Mac while in incognito mode.
Here is a screen shot of it closed:
Here is a screen shot of it when it is opened:
Google is constantly testing ways to embed Google+ in the search results. This seems to be one more test.
Forum discussion at WebmasterWorld.