Either way, as long as he doesn't care that much about what they're doing, you might as well give it a shot. Can't hurt, yeah? [Yeah she gets it, but apathy has its uses too when it's the ENEMY.] Just...make something up about how stupid Katerina's goal is, you're good at bullshitting. Tell him...I dunno, tell him it's for some dumb reason like revenge that she was too weak to get herself or something like that. Anything that would get him to start thinking maybe this isn't worth it after all.

[And she immediately answers his question with a vigorous nod, looking a little relieved.] Yeah, exactly! If he obviously doesn't know, you might as well not bother asking, right? I mean look at how much I wasted our chance to talk to him! Don't make the same mistake!

[Did. Did Undyne just admit to fucking up. To Sans. Is this what friendship with her is like???]