“There isn’t any milk,” says Duchenne.

“I threw it out weeks ago,” says Gail.

“Only there was some this morning,” says Duchenne, “and I said to save it for me.”

Gail snaps her fingers. “Parallel universe!”

Duchenne waits.

“There are infinity of them, you see,” says Gail kindly. “You must have slipped into this one from the one where you had milk. Any other explanation requires us to conjecture some milk-drinking entity, and so is less likely!”

“I think you’re the entity, Gail,” says Duchenne.

“This is also the universe where you agreed to loan me fifty dollars,” says Gail.