In the car the other day, the following interaction occurred.
(My husband and I, sitting in the front chatting, missed the beginning of the kids' conversation.)
Him: Don't say what.
Him: I want to be the last one to say what.
Him: Don't say what!
Her: What. What. What.
Him: Mama, I want her to stop saying What. I want to be the last one to say it.
Him: (whispers very quietly) What.
Her: (also whispers) What.
Me: Maybe you could say it inside your mind, but not out loud.
Him: Quiet for a moment, apparently saying what inside his mind.
Him, to his sister: Haha, you don't know what I just said!
Her, very curious: What?