Kids, there comes a time in your engineering degree where you have to talk about shafts. If you're not a mechanical or a civil engineer, this might only be a very short time, but otherwise, you could end up talking about shafts a lot. The kind that rotate and have stuff stuck to them that generally complicates your previously simple stress analysis questions.
When you should happen to arrive at that special time and place where you have to talk about shafts, the mature engineering student should refrain from giggling like a schoolgirl. Being the wise, mature student that I am, I have gained control over my inner urge to giggle every time someone says "shaft". However, I have discovered today that I am not beyond giggling when a professor pronounces shaft as "shit", then says, "We're going to talk about all kinds of shit today."
One of my more memorable days at work involved a lecture on shaft seals from an aged co-worker, who kept on using his hands to illustrate how the shaft slides through the hole. In, and out, and in, and out. I would have been able to contain myself if it hadn't have been for the repeated use of hand motions.