This story is like a "legend" in my university.

It was the final exam of philosophy.  One of the students
found at the question was so difficult (or so different from what he'd
crammed) that he had absolutely no idea what he should answer.  Instead
of turning in the answer sheet blank, he started writing the recipe for 
making his favorite curry to the most possible details.  Later, the professor
returned the paper to the student.  It said "It's a nice recipe."
He passed the exam!

This story was spread among the students.  The next year, there was 
another student taking the same course from the same professor,
taking the final exam and finding out he was not prepared at all.
He remembered the curry story and he wrote about the curry recipe.
Later, he received the paper returned from the professor.  It said,
"Your curry is missing the egg."  He didn't pass the exam.