Michael: What’s an ego?
Herself: Well, there’s an ego and a super ego.
My sister: A super ego?
Herself: It’s the rules of society that stop you jumping the queue or taking another person’s sandwich. A baby, for example, doesn’t have a super ego.
My sister (faintly): Oh.
On relating this to the Princess’s loving father, he said, “Oh yes, I remember explaining that to her in some context or other. It doesn’t sound like she added much to the original lesson.”