I really think that Margot has developed 'selective hearing.' (She might have learned this from Brodie.)
An example: I'm talking on the phone with a friend this morning, something that Margot just cannot stand (since I'm not paying full attention to her). In my peripheral vision, I see her pick up her plastic bowl of Cheerios and start to drop them in a trail from the living room into the kitchen. Portia followed her, gobbling up the Cheerios from the floor, which makes Margot giggle. She continued to drop them one or two at a time, twisting and turning a trail for Portia to follow, until the entire bowl was gone.
I finish my phone conversation, hang up, and ask, "Margot, what happened to all the Cheerios"?
Margot just gives me a blank look. "Huh?" (I know this is a question she can understand. It's a question she can ask for goodness sakes!)
I repeat, "What happened to your Cheerios?"
More blank stares. She turns and walks away (no doubt hiding a grin).
I feel my parental control rapidly slipping away. (I really didn't think this phenomenon would develop until she was 11 or 12.)