The only response John can muster is a drowsy, affirmative hum, but he's reasonably sure Martin will understand it well enough. He wriggles a bit closer, giving Martin easier access to his own back as he continues to idly explore Martin's. He's starting to drift a bit, lulled by the warmth and by Martin's gentle ministrations, but he lets his mind wander in the general direction of any other itches Martin might have so that his hand might follow, alleviating them one by one.