It isn't difficult to maintain his composure, exactly — they have done this enough, now, for John to have a solid hold on the role he's playing — but he isn't so deeply sunk in it that he can't be touched by Martin's reaction to it all. Not just the alacrity with which he obeys (or promises to, a pledge that may or may not be able to withstand what John ends up doing to him), but the eagerness and the implicit trust Martin displays. That Martin is willing to put himself in John's hands without a second thought... they haven't done this often enough for John to take that for granted. So while he continues to project an aloof air, he can't quite keep his gaze from warming as he looks Martin over and considers his angle of approach.

"Good," he says, lifting his free hand to run a casual, proprietary forefinger along the line of Martin's collar bone and down the V of exposed skin he's just uncovered. He flexes his wrist slightly, just enough to coax Martin into tipping his head a little to one side, and then leans in to nuzzle against the arch of his neck. "The better you behave," he pauses to brush a kiss against Martin's pulse point, "the sooner you'll be free to... attend to yourself."

Perhaps not his best lofty euphemism, but he's learned how to compensate for weaker dialogue. He presses his lips against the soft skin of Martin's throat and begins to suck patiently, gentle enough to not leave any lasting marks. That will have to be earned.