Nappa Berries? He wasn't going to ask, but laughed anyway, and said, "I don't think I've been eating any of those unless the house elves found a secret stash and slipped them into my dinner."
But, wait. Was she saying yes to going to the Halloween Ball with him? Sweet!
"So, it's a date, then. Or, not a date. Whichever you prefer," he replied quickly. Hopefully what he said would make sense to Luna, if it wouldn't to anyone else. Ravenclaws usually got things at least.