He laughs a bit--and it sounds more real this time, an indication that he understands. But it's a nervous sound, too, and he doesn't seem entirely comfortable with the sentiment behind the words.

Still, Jack waits. Not very long, but he watches her eyes close and her breathing slow. He's not sure if she's asleep or not by the time he stands up and finds another part of the medbay to haunt, but either way, the sentiment is there.