Surprised, yes, that was a word. Confused, incredulous, astonished... He could understand it, a little, looking back. Who wouldn't want to have a secret identity, to walk around without anybody recognizing you, from time to time? Not that it was all that secret. Anybody who looked at the giant bone canine recognized the similarity to Sans' smaller companions. The way all their skulls resembled the blasters, the way they were skeletons. So maybe that wasn't Sans' reason.

"...Sans doesn't tell anybody a lot of things," Papyrus finally replies. "And he's just gotten worse, in the time he's... been here. Thinking I was dead."

Or as good as dead. Trapped in a loop in time with everybody else, where sometimes he died and sometimes he ruled and sometimes he got to keep hanging out with friends, and none of it got to last. Even the people Papyrus left behind, alive, don't quite feel real to him. Not with knowing that he'll eventually go back to a time they don't remember.

He shakes his head, and hastily adds, "b-but he told me now. And I'm sure he'll tell me more, as he's able to. So nevermind that stuff!"