There is nothing more revealing than a student's question. My all-time favorite Geometry question came after I had completed a fairly lengthy proof on the overhead: "Ms. A, I was able to follow every single thing you did. What I don't understand is, how did you know what to do?"
One of the characteristics of a top-notch geometry student is their broad repertoire of geometry postulates and definitions. The next step, then, is to ask this question: "What do I wish were true?"