One night my friend Erin went out to the cinema, leaving her husband Michael in charge of their young son. Michael duly fed and watered the boy, read him a story and tucked him into bed. As was the family's routine, Michael then kissed his son goodnight and moved to the door where he dimmed the lights so that the room was almost, but not quite, completely dark.
"Goodnight, Daniel," he said.
"Goodnight, Dad," said Daniel. "Goodnight, Mum."
"I told you, Dan, Mummy's not here. She's gone to see a movie."
"But she is here!" the boy insisted.
"No, silly," said Michael, moving back into the doorway. "Mummy's out for the night. You'll see her in the morning."
"Oh." Daniel bit his lip thoughtfully. "Daddy?"
"If Mummy's not here, whose hand is that on your shoulder?"