His expression went blank. Oh, he realized, all right. He was a genius, the Doctor, and what's more, he knew Rose. He knew when she was trying her best to gently make a point to him. That was another thing she did better than anyone, pointing out the obvious that he'd missed by being too close to it to see it.
They were fictional. Not just the stuff of legend, he and Rose, but fiction. People from stories that had been handed down not by people who had met them and told the tale, but by people who imagined them out of nothing.
"What?" he squeaked, because really, what else was he supposed to say?