A Jew who was unemployed for a long time decided to open his own medical clinic. "A cure for your ailment guaranteed at $500; we'll pay you $1,000 if we fail."
A doctor thinks this is a good opportunity to earn a $1,000, and goes to the clinic.
Doctor: "I have lost my sense of taste."
Jew: "Nurse, please bring the medicine from box 22 and put 3 drops in the patient's mouth."
Doctor: "This is gasoline!"
Jew: "Congratulations! You've got your taste back. That will be $500."
The doctor gets annoyed and goes back a couple of days later to recover his money.
Doctor: "I have lost my memory, I can't remember anything!"
Jew: "Nurse please bring the medicine from box 22 and put 3 drops in the patient's mouth."
Doctor: "But that's gasoline!"
Jew: "Congratulations! You've got your memory back. That will be $500."
The doctor leaves angrily, but returns several days later more determined than ever this time to make his money back.
Doctor: "I've lost my eyesight."
Jew: "Well I don't have any medicine for this. Take this $1,000," passing the doctor $500.
Doctor: "But this is only $500!"
Jew: "Congratulations! You've got your eyesight back. That will be $500."