My Dad was a pretty wise man who was wont to note that very few people frown when they're eating chocolate. It's true. It's also true that if you bring a class of people donuts for their final exam, most of them will smile and enjoy a donut. The smile seems to last even longer than the donut.
It's also true that if you leave the leftover donuts in the department lunch room, they will disappear, but people around the department will also be smiling more.
If you have a few essays left to grade, and plan to grade them during the first part of a class's final, it is a well-known truth that the first person to finish will be the one whose essay is on the bottom of your pile.
It's WAY cool when you read one of those papers, and it's so good you want to laugh. It's a little weird to have a whole class of finals-takers look up to figure out why their professor's laughing, though. I read a couple of very good finals today; I don't know that I taught these folks anything, but they sure learned stuff somewhere! What's best is that they learned to put things together in interesting ways that make sense and make me think.