We got out the tiny little wave tank, which is so worth it, since I use them so much more than I would ever use the old larger wave tanks. We saw just how much more difficult it would be to draw the waves. We then went out into the hallway, held hands, and shows how the waves change direction when you go from a faster medium to a slower medium. I like emphasizing that we use this more difficult model because we can predict more using this model.