Chalk Talk

I was working in the garage yesterday while Claire and Elsa were drawing on the driveway with chalk.  I heard Elsa say, "We need more bird poop."  What a delightfully unexpected phrase.  I went out and asked her why.  Her rather logical response: "We are drawing on the bird poop.  Do you want to know why?  Rain washes away our chalk.  So if we draw on the bird poop, the rain will wash it away too."