Why I seemingly laugh at nothing sometimes

My school still does homeroom. During lunch, another teacher who doesn't have her own room has her homeroom class in mine. Sometimes while I eat, I pretend to be entering grades at my desk, but really I'm watching her students.

Today a boy sat not too far from me rolling his pencil back and forth across his desk with an expression on his face that looked as though he himself was falling off a very large cliff. I immediately thought of Bri on Friday and her story about the boys in her class that furiously rub the tip of their pencil on their desk and then touch it on their cheeks and hands to feel the heat, yelling "ouch" in a tone that would indicate it was just as shocking as the first time they tried it. She added that they do this all day.

The image of Bri telling this story combined with the thought that we actually teach humans who do these things made me laugh out loud during homework time. I tried to stifle it without much success. That boy rolling his pencil stopped and looked at me like I was insane for laughing at no reason whatsoever.