Correctly answer nine out of twelve bonus questions.

To unlock SuperStiff mode easily, play through the level as usual. When the bonus question appears, guess it as normal, but write down the correct answer. Do this until you get to question 10. if you have not already unlocked SuperStiff mode, quit the level and play it again. Now that you have the answers to the bonus questions, choose the correct answer and the Flash-O-Meter should disappear after question 9.