Bill and Steve were seated next to each other while taking a test. When they had finished, the teacher called them up to her desk. "Sorry boys," she said, "but both of you will be receiving a zero on the test."

"But, why?" they asked.

"Looking over your answers and noting how very alike they are, it is obvious that one of you cheated and the other one let him do it," replied the teacher.

"That could just be a coincidence, Miss Ames," Bill said. "What would make you think we cheated?"

"Well," the teacher replied, "I might have believed it was a coincidence if it wasn't for the fact that when you got to question number 8, Steve wrote 'I don't know' for the answer, and you, Bill, wrote in 'darn, neither do I'."