Nina's own giggle was pretty weak, and she wasn't going to let go of him, but she did manage to retort to that with, "You can just make me another."

Because, please, now that she knew he could make milkshakes as if she wasn't going to take full advantage of that.

"And... and you said I hadn't known, in that other future. And we're unbreakable. So I'm going to find a way to cure you."

Because, obviously, he was terrible at studying. Nina was much, much better at it. He must have missed something.