[There's a few reasons for his enthusiasm about the picture. People to look forward to remembering, rediscovering whatever cherished memories of friendship brought them together... And one of whom is right here! Plus a picture of Papyrus himself, which he didn't already have.

And partly, it's comforting to see evidence of his existing before what he can remember, standing and conscious and smiling. Proof that he's not a reanimated pile of bones. Which, obviously, was a completely absurd idea. He's seen an example of reanimated bones, and they're not nearly so personable! But between Michael and Ogata, it was one of the first ideas anyone gave him, so it's stuck with him.]

Yeah, we definitely... did...

[Papyrus hesitates as he squints back at Sans, having only just caught the staring. Somehow, unlike when other people stare at him, he doesn't get a creepy feeling until he's consciously noticed the stare. Is he, on some subconscious level, just that used to this guy looking at him...?]

But the details are, uh, eluding me a little bit. We might have to look for reminders... Or get to know each other again.