Once upon a time there was a doctor who took his apprentice with him when he made his visits. One day while visiting a patient, the doctor said: "Why do you not listen to my orders that you are not to eat anything?"

The invalid said: "Sir, I assure you that I have eaten nothing."

"That is not true," answered the doctor, "for I have found your pulse beating like that of a person who has eaten grapes."

The patient, convicted, said: "It is true that I have eaten some grapes; but it was only a little bunch."

"Very well; do not risk eating again, and don't think you can fool me."