Jon and Dan are in a mental institution which has an annual contest that picks two of the best patients and gives them two questions. If they answer correctly, they are released.
Jon is called into the doctor's office first. The doctor says: "Jon, what would happen if I poked out one of your eyes?"
Jon says: "I'd be half blind."
"That's correct. What would happen if I poked out both your eyes?"
"I'd be completely blind." The doctor tells him that he is free to go. On Jon's way out he tells Dan the questions and answers.
The doctor asks Dan: "What would happen if I cut off one of your ears?"
Dan says: "I'd be half blind."
The doctor, slightly puzzled, continues, "What would happen if I cut off both your ears?"
"I'd be completely blind."
"Dan, how can you explain that you'd be blind?" asks the doctor.
"Well," replies Dan, "my hat would fall over my eyes."