The "secret" feature is called the Google Wonder Wheel. It comes up with several variants of your selected keyword.
Some say Google will rank you higher if you use those keywords but do not take my word for it.
To access it type into Google your main keyword phrase then on the side you should see this:
Thats it. Now you are on your way to tapping unto unknown keywords right inside Google.
What do you think of the Google Wonder Wheel?