Natural Phenomena

I can imagine it's only going to get tougher to explain. Last night, a glass was sitting on the kitchen counter as the sun was going down, and a rainbow ended up being reflected onto the floor. Avery kept saying "What is it?" even though she knew it was a rainbow, as she recognized it and said "Rainbow!" immediately. I took the "What is it?" to be more of a "Why?" or "Where does it come from?" kind of a question, so I tried to explain it to her, and she just looked at me dumbfounded. Here are some pictures: