When I was doing my undergraduate degree in biochemistry at Concordia University in Montreal, there was a Russian teaching assistant called Alexei. One day during an organic chemistry lab, he told us a story that has remained tattooed on the inside of my skull ever since.
When Alexei was doing his undergraduate degree at the University of Moscow, there was one particular professor who had the bad habit of coming to class drunk some times. It was easy to tell when he was drunk: if the blackboard was covered with incomprehensible scribbles, he was fine. If he was trying hard to write legibly, he was drunk. That day, he was drunk.
The class was given in a large auditorium with 2 doors on either side. The professor was writing on the board when suddenly, the last piece of chalk broke. Just that moment, a student entered through the right door, also drunk. The professor called to him: “Young man, can you go to the other classroom and get me a piece of chalk?” The student goes back out, reappears a minute later through the left door, and says: “Excuse me, do you have an extra piece of chalk, by any chance?” The professor replied that he did not. When the student came back through the right door, he reported that he couldn’t find any chalk. The professor said “Yes, I know, one of their students just came looking for some.”