Easy, I thought.
"You know the long thing that Nikita and Dashiell have on their bums. The long thing that wags? That's a tail."
"No, mama. What does tail mean?"
"It's the thing on the dog's body they wag."
"No! What does tail mean?" he asks with increased emphasis, letting me know he is not accepting this definition. He does this a lot too. So I try my old fallback.
"Hmm. I don't know. Maybe you should ask papa."
"Yeah, he's a scientist!" adds Big Dog. They're pretty impressed by Mr. Dog's profession.
"That's right," I say, "He can probably tell you."
They sit quietly for a moment, possibly mulling their father's scientific brilliance, then Big Dog speaks, his voice full of scientific aspirations. "I hope he discovered dog butts."
And I just didn't have the heart to shatter that dream.