Adding mint Mentos candy to a two-liter bottle of Diet Coke produces a fountain of soda foam that can reach 3 m high. A demonstration such as this can get a “Wow” out of most audiences, usually followed by a “Do it again!”—but can it be used to teach anything? The answer is a definite “Yes,” and what follows is a guided inquiry activity that allows middle school students to do this experiment inside (with a minimum of mess). This activity, in its simplest form will provide middle school students with a safe and fun example of what happens when matter changes states, and a better understanding of scientific inquiry, including the development of a hypothesis, the development of experimental methods, and the interpretation of data.