There was a professor in the Chemistry Dept. that I did graduate work in who was noted for the difficulty of the tests he gave.

There was a professor in the Chemistry Dept. that I did graduate work
in who was noted for the difficulty of the tests he gave. His first
name was Percy. On the morning of a test he walked into the lecture
hall to find the class very quiet and very diligently studying their
notes for that last fact for the test. It wasn't until he had walked
up the aisle to pass out the tests and turned around that he saw the
message emblazoned on the blackboard in big chalk letters :
MERCY PERCY !
To which he replied :
Alas Class !