Mine!

Gavin: (Grabs a medicine bottle hides it behind his back) "Mine!"
Me: "No it isn't."
Gavin: "Yes Mine"
Me: (Taking it quickly from him) "No it isn't yours."
Gavin: "Yes MINE!"
Me: "If it's yours what is it?
Gavin:"What is it?"
Me: "If you don't know what it is it isn't yours."
He gave up and walked away!