Funny joke, probably true too.
I've taught students of all ages oral class in China. Asking them to answer your questions in class sometimes has smelly consequences - it makes them fart. Boys are more likely to fart than girls, but both genders can produce foul smells when put in the spotlight or on the spot. So, don't get too close to them when you're doing your job. Maintain a safe distance, say at least three metres from each student you ask a question of, especially during oral tests.

Bit course I think.