Yeah, he's seen that expression before, on occasion. Not usually directed at him, though. Some things, Sans knows entirely too much about him to have any cause for that look. Other things... Papyrus has gone to a lot of trouble to cultivate his privacy, and if that means throwing other feelings and worries out like detritus to distract, then so be it. Now, though, he's too tired to manage any such deliberate trickery, too tired to enthuse about decoration plans, and too tired to really make sense of everything for anything like a coherent description.

Instead of answering right away, he hugs at himself with one arm, the right clasping at the left just to affirm that he can. "...I don't know. It was dark. I don't... remember, going anywhere." Not that this necessarily means much, when he's been having deja vu and forgetfulness since whenever Sans found him. His hand tightens again.