Flog shows you the most torturous code you wrote. The more painful the code, the higher the score. The higher the score, the harder it is to test.
Run it against your best stuff. I double-dog dare you.
Flog essentially scores an ABC metric: Assignments, Branches, Calls, with particular attention placed on calls.
Run flog on all your code. Try this:
find lib -name \*.rb | xargs flog
Whatever is at the top of the report is worth looking at.
This is how it works: