He wasn't nearly as loud or outgoing as those Gryffindors tended to be, which was what she was probably used to. Fred and George were starting to rub off on him though, so if he had been completely awake and energized, he might have had something to say to her about keeping quiet.
As it was, he was glad he was quiet the second he saw what she wanted to do. A grin had started to form on his face when his brain caught up with her actions and his hands dropped the fireworks that he had been handling.
His hands, now free, pulled her closer. One hand found itself to her waist, while the other wound itself around the small of her back.