examining primary themes of results to guess at unsurfaced terms related  to search

before:
![image](https://cloud.githubusercontent.com/assets/447559/5215598/d2e1450c-7620-11e4-8e65-2d70299ebb4a.png)

after:
![image](https://cloud.githubusercontent.com/assets/447559/5215600/dbac678e-7620-11e4-9d4e-b1aa81cb43af.png)