Woof

Everyone's favourite, what more can I say? How about an anecdote from Peter White, a blind man who doesn't use a guide dog:

On the Tube, just got on a train.
Man in carriage "'Ere mate, where's yer dog?"
Peter (in a moment of devilment):"Oh? Isn't he here? I must have left him outside"
Man: "Don'cher worry, I'll sort it!" Yanks the emergency stop.