LD: The tree outside is shimmering.
ME: Oh, that's cool. What is that?
LD: It's the pool reflecting on the tree.
ME: Nice. So. What is it that is actually reflecting on to the tree?
LD: What do you mean?
ME: The tree is shimmery, and it is from the pool, but it's not water that is on the tree, right?
ME: So what is it?
ME: (silent stare with eyes widened)
LD: Oh! Light!
ME: Exactly! And where does the light come from?
LD: The sun!
ME: And where does the sun get its light?
LD: (silence) ........um.......
ME: The sun is a star, right? So where does a star get its light?
LD: Ummmmm...... ( suddenly the tension in her face releases) God and Jesus! That's my answer.
We could talk about nuclear reactions in a star, but at some point in the backwards questioning of "why" we all have to come up with some regress-ending explanation..... or shrug our shoulders.