"Stand in the middle."
"In the middle of what?"
"In the middle of the picture."
"What picture? I don't see any picture."
"The picture I'm about to take."
"You're about to take a picture?"
"Yes, I'm going to take a picture."
"But you don't have a camera. How can you take a picture without a camera?"
"I'm going to go buy a camera."
"And you want me to stand here while you go buy a camera?"
"So I'm supposed to stand here and do nothing while you go no telling where for no telling how long to buy a camera then come back and take my picture, as if I've got nothing better to do than wait on you. Does that sound about right?"
"What part did I get wrong?"
"I'm not going to take your picture."
"No, I'm not."
"So why do you want me to stand in the middle of the picture if you're not going to take my picture?"
"To mark the spot, Silly. Otherwise I might not come back to the right place."