> All cell phones must be turned off before the movie will begin. > Oh wait, nobody in the audience has a cell phone. Can the movie begin? That's a really goo

> All cell phones must be turned off before the movie will begin. > Oh wait, nobody in the audience has a cell phone. Can the movie begin? That's a really good one. Admittedly, I've never had to actually explain why statements can be vacuously true to anyone. But I'll keep this in mind if I ever have to.