"You'll love that," Joan says to Sherlock. "I know you enjoy teaching."

"A child is different from a protégé, Watson," Sherlock says.

"Not that different. You just need some extra patience. I've seen you train roosters. I'm sure you can manage a ten year old."

Sherlock scoffs again, and again it's more amusement than anything else.

"Just don't teach him how to pick locks," she says with a smile. "Or hotwire cars. Non-criminal activities, please."