[Sans holds his ground even if he's still not quite looking directly at Papyrus. He doesn't know how much of this Papyrus is deliberately ignoring and how much he didn't realize, which leaves Sans to have to state everything out loud. He hates doing that.]

That invitation was already cuttin' it close about being too obvious. There's no way the people in charge aren't watching the net, so if you start talking about an invitation for all of us to meet up having puzzles in it, they might look closer.

[And it really wouldn't take looking very close to figure it out. Sans is going, but he knows he's taking a risk. He needs to see who else is in this situation.]