[Papyrus's continued uncertainty is enough to make Sans continue overthinking the whole situation. He is sure about this, right? He's definitely sure. False memories are a thing, but not like this, right? He still can't remember anything about Papyrus specifically, but he can't remember anything at all before he ended up working for the Bureau, and even those memories are spotty. Papyrus has to be his brother, that's just--it's true. It has to be true. He's sure it's true.

He needs to stop thinking about this. He tries to push it away, focuses instead on what else Papyrus is saying.]

Some people seem to remember things just by bein' around people they knew, or seein' stuff they saw before, so it can't hurt.