A salesman's car breaks down, so he asks a farmer to let him spend the night, and the farmer agrees. In the middle of the night, the salesman wakes up and is really thirsty, so he decides to go to the barn and get some milk from a cow.
Soon, the farmer hears noises coming from the barn and goes to investigate. He then sees the salesman coming out of the barn soaking wet and with a white liquid dripping down his face. The farmer asks, "What happened to you?"
The salesman says, "I just got thirsty, so I milked your cow. It was so dark in there I don't know how I did it. But I'm telling you, that cow has great milk! I must have drank a gallon of it!"
The farmer then stares at him with a puzzled look and says, "But we don't have a cow. We just have the bull..."