The Doctor was almost disappointed. He'd been looking for a bit more of a challenge. (For his part, the Time Lord wasn't overly concerned about the fact that they didn't know what they were questing for. Sometimes, the journey mattered just as much as the destination.)

He grinned at Billy. He would have corrected him if he hadn't been happy with answer he'd drawn in the air, of course, but it wasn't necessary. He was clearly a very intelligent human.

"Go on then."