That's what's called the Achilles Heel, I said, and told her the story to distract her. Achilles was the greatest hero of the Trojan war, I explained, because he could never die -- arrows just bounced off him. When he was a baby, his mother dipped him in the Styx, a magic river --
"A magic river?" she said sceptically.
Just go with it, I said. And anyone who went in the river couldn't be hurt, so she dipped him in when he was a baby. But she had to hold the baby upside down to dip him in, so there was one part of him that was left vulnerable.... his heel.
And one day, I said, when Achilles had grown into a man and become the greatest of the Trojan warriors, his enemy shot an arrow into his one weak spot -- his heel -- and killed him.
"Why didn't she just dip his heel in too?"
Well, she was holding him by the heel ...
"Why didn't she dip her hand in?"
Well, perhaps she would have fallen in if she had reached any further ...
"But then she would have been a superhero too," The Girl said.
Yes, well ...
"And why didn't they just bring all their friends to the river? And why would he die from an arrow in the heel?"
Um ... it was a poison arrow, I said.
"And why ..." The Girl wasn't buying any of this.
Does your heel still hurt? I asked.
"No," she said.
Good, I said. Let's just leave it there for now, and I'm glad you can ask so many questions. With some of these oldest stories, though, the point is not to believe the story really happened, but to learn the lesson in it.
"Dip your hand in all the way," The Girl said.
Um ... yes, we'll go with that.