We have seen many variations of expandable sitelinks over the past with our Google Sitelinks coverage, but here is a new one. Tom Whiley spotted one that not only expands, but gives you a teaser snippet each individual sitelink expandable section on why you should click that little arrow to expand it to show more links.
Here is a screen shot from Tom on Twitter:
There have been so many variations of this design, it is hard to know if this is the first time Google is testing this specific application of sitelinks user interface. Either way, I do like the snippets within the sitelinks, it does give the searcher a bit more knowledge of what is beneath those drop downs.
Forum discussion at Twitter.