Google can help assist you with your search queries.
Which keywords does this tool activate for? Who knows, certainly not me. But let’s take a look at the search below to see how Google is helping this user,

I cannot be sure if this is new or if it’s been around for a while, but it’s the first time I’ve really noticed it. I have seen it in the footer below, but I had never noticed it right there directly below the ads and query.
Aww gee, Google is so helpful!

February 19th, 2008 at 6:34 pm
It looks like a custom search engine or co-op refinement.
http://www.stonetemple.com/articles/custom-search-engine-topic-refinement.shtml
has a nice section on these.
- Phil
February 19th, 2008 at 6:45 pm
I feel it’s a little more than that though. I know it wasn’t a CSE because it was on google.com and I wasn’t logged into an account.
I have updated the article with the search query I used (sorry, I forgot it originally.)
February 19th, 2008 at 10:16 pm
It looks like this is part of an ambitious plan to improve the quality of and access to medical information.
http://www.youtube.com/watch?v/IPj3oRBYOUw
An explanation of the links is at about 4:30
Another source is:
http://googleblog.blogspot.com/2006/11/health-care-information-matters.html
“Google and the health community have labeled sites and pages across the web making it easier for users to refine their health queries and locate the medical information they need. Do a search on Google about a medical issue or treatment like diabetes or Lipitor and you’ll see some choices for refining your query, such as ’symptoms’, ‘treatments’, and so on.”
February 19th, 2008 at 11:49 pm
Phil,
Ah good call. I forgot about that. Thanks for the heads up, I appreciate it.