A visitor to San Francisco is standing on a street corner waiting for a bus when he notices a blind man and his guide dog. The dog leads the man into the street, where he is brushed by an oncoming car. The man is knocked down, and he rather gingerly gets back up. He calls the guide dog over, reaches into his pocket, pulls out a doggie treat, and gives it to the dog.

The visitor, upon seeing all this, walks over to the blind man and says, 'That's amazing! Your guide dog led you into a busy street where you were nearly run over by a car, and yet you're giving the dog a treat. You must really love that dog.'

The blind man turns to the visitor and says, 'No, I'm gonna kick the dog's ass - I'm just trying to learn which end is which.'