He didn't greet her with a suplex or anything, it can't be that surprising, can it? Papyrus might be desensitized to surprises. It comes from living with Sans "woopie cushions" the Skeleton his whole life.

"Oh my god? Instead of passively reading the story... you experienced it... first hand?" He gapes, delighted by the prospect. "I wish there were book monsters who could do that back home! It'd be even better than television..." Better than most shows, at least. There was one channel that even the most immersive of comic books couldn't top.