One afternoon the boys were playing outside. I was inside doing something significant like
S: Oh, we're building a castle outside out of rocks.
Me: Great! Have fun!
And I left it at that. It was only later that I went out to check on them and realized the gravity of the situation. They were, indeed, busy building a castle. But what he neglected to mention was that the "rocks" were pieces of brick that they were chipping off of the side of the house with a hammer! (They had actually done enough damage that M later had to go back and fill in the entire area with concrete!)
*note: Do not try this at home... photo is a simulation borrowed from pirateplanet.