Nuffing

This conversation happens at our house more than I would like to admit. And yes, I do watch my children. If you can't tell, the picture is taken from our couch as I was/have been sitting there for a few months puking my guts out.  That might be why this has occurred a lot more lately.

(An unusual, long silence)
Me: "Llllluuuukkkke?!"
Luke: "What Mommy?" (As he runs to me from around the corner or another room)
Me: "What are you doing?" (Evidence is clearly written all over his face)
Luke: "Nuffing."