"Any time," Jack said back, smiling at him like he had a coat-hanger stuck in his mouth.

He nodded, belatedly, in response to the Doctor's idea about the drug. "Self cleaning too," he agreed, "if someone else doesn't finish the job it'll finish it itself. Very clever. Sort of thing a few people I've known would just love to get their hands on."

Shifting slightly, he settled the Doctor a little more comfortably in his arms and glanced at the mouth of the cave and back to the Doctor with a warm smile.

"Well then?" he joked, pretending to check a watch that wasn't there. "I'm waiting for that kiss."