It's not like Frisk has really registered that this isn't a private conversation, either. It would take a lot more thought and focus than they have to spare on that reality for them to become fully conscious of it.

Heck, it had taken two whole weeks before they stopped trying to talk to Chara off-hand when they first arrived.

That information, however--

"What?!" Frisk helps and nearly jumps, their grip tightening on Chara's hand for a moment. "But--that's horrible! Why would you do that?!"