There was once a skillful doctor with a young assistant. Next door lived a farmer. "I may be a farmer, but I'd really like to study medicine," he said.
"Please take me as your pupil," he begged the doctor.
"I'm sorry, I don't accept students," the doctor replied. In those days, the medical profession was passed on from generation to generation and rarely taught to outsiders.
"That's it!" the farmer thought. "Doctors always teach their students at night. I can hide beside the window and listen in."
That evening . . .
"They've already put off paying for a long time," the assistant said. "Do you want to charge interest?"
"Just collect for the diagnosis and the medicine," the doctor said. "you can forget the interest [suan li k'o chih]."
The farmer, who only heard the last four words, misunderstood the doctor as saying, "garlic can cure dysentery," which is pronounced exactly the same.
"Aha! So garlic relieves dysentery!" he exclaimed.
It so happened that a relative of his who lived some miles away was having stomach troubles, so the farmer set off to have a look. He told his relative to eat garlic, and strangely enough it worked.
The farmer stayed on at his relative's house and started a practice curing dysentery. The treatment worked on all his patients, and the farmer's reputation soon spread far and wide. When the doctor heard of it, he came to pay a visit.
"I hear you have a cure for dysentery," the doctor said. "Who taught you?"
"Well, actually it was you!" The farmer told him how he had eavesdropped on him that night.
"Ha, ha, ha," the doctor chuckled. "We were only talking about a medical bill of mine."
"Was I just fooling myself? But then why does the treatment work?"
"Well, you must be smarter than you look, so I've decided to take you as a pupil."
The treatment may have been based on a misunderstanding, but since it turned out that it really works, garlic has been used as a medicinal ingredient ever since.