Ive noticed there isnt any talk about the brief period between the colors appearing and sans being slashed What happened there? Was the, er, fog dispelled and Papyrus didnt actually need to kill Sans but did cuz he didnt know that?
no, if papyrus wasn't going to kill sans, then sans wouldn't have been able to recognize him.
strictly via text interpretation, sans might not necessarily recognize papyrus until the attack lands. like, obviously something has shifted that sans has reacted to, but it is entirely possible that he doesn't yet see who his attacker is until the hit lands.
It is entirely possible that Papyrus changed tactics, and said something different from the previous [Identify] acts that was enough to shock sans into lowering his guard. Clearly he's been speaking to the other characters... but just because we can get the gist from their replies, doesn't mean we know what he said.
