Lucy blinks at him. At least that's something a snake can do easily.

"Only occasionally," she answers honestly. She probably sees Peter in a good mood more often than other people do. And when he's in a bad mood, she often joins in with the complaining. So there's really only when she can't be bothered to listen to him whine that she tells him to suck it up and stop sulking. "Did the TARDIS say you do, or..?"