Start each class with a U-tube challenge. What happens when water is poured into the left tube? Change the tube configuration and ask the same question. Wow, some students have major misconceptions! Ask them to suggest ways for the liquids to be at different levels. More than a dozen challenge questions are suggested. Developed and used to develop critical thinking skills from middle school to Advanced Placement, Ron Perkins treasures his best answer: 'Mass Hypnosis!.' This is analogous to the famous Niels Bohr Barometer Story.