Luke (reading): Sandstone is one kind of sedimentary rock. It is made of grains of sand, mud, and.... pue.... puh.... puddles?
Me: Try again.
Me (snickering): Are those D's?
Me: Almost. Is that a U?
Luke: Pebbles! What is a pebble?
Me: What do you think it is?
Luke: It's a little rain drop that makes a puddle.