DD4: "I bet you didn't know that I didn't know that you could do that."
Me: "What?"
DD4: "I said I bet you didn't know that I didn't know that you could do that."
Me: "What are you talking about?"
DD4: "Are you having trouble with the double negative?"
Me: "What?"
DD4: "Oh Mommy, never mind."

I still don't know what she was talking about.