The young trainee was greatly impressed by the doctor's swift diagnoses as she accompanied him on his house calls. 
"Your trouble is too much alcohol," he told the first patient. "Give it up, and you'll be fine."
At the next house, he told the patient: "Your trouble is too much chocolate. Give it up, and you'll be fine."
The trainee asked the older doctor how he did it. "Simple," he replied. "I just pretend to drop my stethoscope, and as I stoop down to retrieve it, I have a look under the bed. If there are empty bottles there, I know they're drinking too much. If there are food wrappers, I know they're eating too much. You try it."
So at the third house, the trainee examined the patient, dropped he stethoscope, looked under the bed, and pronounced: "Your trouble is too much religion. Give it up and you'll be fine."
"How did you make such a strange diagnosis?" asked the older doctor as they left the house.
"Well," said the trainee. "I dropped my stethoscope as you said. And under the bed was the parish priest!"