One day Pete was complaining to his friend "my elbow hurts. I better
see a doctor". His friend said "Don't do that. There's a computer in
the drug store that can diagnose anything. It's quicker and cheaper
than visiting a doctor. Simply put a urine sample in the machine and
it will diagnose your problem and tell you what to do about it. It
only costs $10.00." 
Pete figured he had nothing to lose so he filled a jar with a urine
sample. He went to the drug store. Finding the computer, he poured in
the sample and deposited $10.00. The computer started to make a weird
nose and various lights began to flash. After a brief pause, a small
slip of paper printed. It said: 

You have tennis elbow. 
Soak your arm in warm water,
avoid heavy labor,
it will be better in two weeks.

Later that evening, while thinking how amazing that computer was, Pete
began to wonder if it could be fooled. He decided to give it a try.
He mixed some tap water, a stool sample from his dog, urine samples from
his wife and daughter. To top it off, he masterbated into the concoction.
He went back to the drug store, poured the sample into the machine and
deposited $10.00. The machinhe again made the usual noise and printed out
the following analysis: 

Your water is hard,
get a softener.
 
Your dog has worms, 
get him shots.
 
Your daughter's using cocaine,
get her into a rehab clinic.
 
Your wife's pregnant,
it's not yours,
get a lawyer.
 
And if you don't stop jerking off, 
Your tennis elbow will never get better!