A successful proctologist decides to fulfill his lifelong dream: give up medical practice and become a Harley mechanic. 

He enrolled in mechanics school and after many weeks of training he has to pass the final examination which is taking apart and then re-assembling a randomly chosen Harley engine.

He grabs his tools and sets to work, but soon gets worried: he is still working on the valve covers while everybody else is already removing the cylinder heads.

He falls more and more behind, and just as he starts to put it back together, the last student gets checked off & walks out of the testing room.

He finally manages to put the engine back together.

He couldn’t sleep that night because he was worried about his score since it had taken him so much longer than everybody else.

The next day the scores were read out and worriedly he listened to the teacher finally call out his name.  "Well," the teacher says, "out of one hundred possible points you scored 150."

"But how is that even possible?" the ex-proctologist asks.

"Well, hears the breaks down: You get fifty points for correctly taking the engine apart. And you get fifty points for putting it back together perfectly."

"And what did I get those additional fifty points for?"

"For doing it all through the exhaust pipe."