"Okay, good, now smile!"
"No, seriously, come on! Smile! Pretty please?"
(Sigh.) "Okay." (Drastic times call for drastic measures.)
"Don't you dare smile."
"I'm totally serious. Don't smile one more time!"
"No really, Kid A, if you smile again you're going to be in trouble." (Pretend stern voice)
"Hey! What did I say (erm, could you move over by this wall... the light's better...) You're still smiling! I SAID STOP."
"Oh boy. You are just in the biggest trouble ever."
And there it was, the shot below, the one I wanted. You just have to be creative, to get around my contrary son at times. And now you know my dirty trick.