An aging hypochondriac has the strange notion that he is dead. His delusion, in fact, becomes such a problem that his family finally pays for him to see a psychiatrist.
The psychiatrist spends many sessions trying to convince the man he is still alive, but nothing seems to work. Finally, the doctor tries one last approach. He takes out his medical books and proceeds to show the patient that dead men don't bleed. After hours of tedious work, the doctor asks him, "Do you now agree that dead men don't bleed?"
"Yes, I believe I do," the man replies.
"Very well, then," the doctor says. He takes out a pin and pricks the man's finger. Out comes a bead of blood.
"What does that tell you?" the doctor asks.
"Oh, my goodness!" the man exclaims, staring at his finger. "Dead men do bleed."