The Doctor had long since learned that some regenerations were more sensitive than others. Also that almost all of them seemed to have especially weak spots and given that he felt somewhere between just melting and wanton moaning at Jack's treatment of his neck, he was fairly sure he had an inkling what spot it might be for this one.

There was something close enough to a moan before he managed to bite down on his lip. He rolled to the side, away from the vicinity of Jack's all too talented mouth, but keeping his arms around him to not make him feel rejected. He just wanted to be able to think. "Gods..." Yeah, his focus was shot. "Starting to see your point about it being hot here. Now I could use more ice cream." But he was actively teasing here, as his grin and the way his tongue flicked out to wet his lips indicated.