A simple demonstration used is a corner cube, retroreflector.  A palm sized corner cube can be held at eye height facing a group of students who have not decided that they want to engage in the demonstrations. The students are asked “Whose eye do you see and how do I know it an eye?”. This works best with 3 – 5 students so each can see the input face of the cube corner. As they begin to identify their friend’s eye they will start to observe that one see the frame from glasses. Suggestions are made to cover one eye and evaluate what they see. In short order they see that each eye is seeing itself and the device can be explained as to how the incoming ray direction matches the outgoing direction though 3 reflections. At the end of the demonstration students are asked where this device is used.  Each student has seen plastic bike reflectors and roadway markers completing the demonstration’s goal of concept to context.