Google Search is testing a new search feature that lets you filter the search results by pages that also mention specific words. Google adds a box to the right of the search results page that lets you check off those words and then Google will highlight those results on the search results page.
Carrie Hill shared some screen shots of this on Twitter, you can click on them to enlarge.
Here is the filter box:
Here is what happens when you filter them:
I personally cannot replicate this but this is interesting.
Forum discussion at Twitter.