There’s a conversation that happens in the second panel.  Two family members can, if not know what the other would say, assume that they’re saying the opposite of each other anyhow.

The argument isn’t going to change either one’s mind.  It’s just so that one of them (Each assuming they’re the one) will get to say, “I TOLD YOU SO” later on.

 

Odd. I think I may have used this concept in an earlier cartoon.  Or two.

 

Or forty.