[Oh, he knows full well. He doesn't need to see her expression to tell that much.

He does need to get a read on Aang, however, hence why the airbender is getting all of his attention.]

It's risky. Especially if he surprises you with a face-to-face. He has... well, there's an ocular ability he likely has. It lets him see what the two of you call chi.

[Katara can probably see where he's going with this.]