Me: How was school today?

DS6: Good, I am studying erosion.

Me: (thinks about curriculum, not sure where erosion would fit) Is anyone else studying erosion?

DS6: No, everyone else is playing tennis then. I noticed it looks like there is an erosion problem near the tennis court. If they don't do something about it, I think one corner of the court might start crumbling soon. I just don't know how quickly it is eroding.

(Found him outside later experimenting pouring water on a dirt mound)