My memory of my primary school life has been fuzzy. Of the few fragments that I remember, there were those wooden tables that we used at school, unlike perhaps the fine furniture students use today. The surface though smooth, was uneven. You could trace the texture of the wood and you could see the little holes of various sizes scattered over the tabletop. If you had a wide imagination like I did, you would picture the surface of the table as the terrain of an unknown planet. You could even draw a map and name the craters.
In my primary school days, we used pencils and rubbers often. Instead of brushing the residue of the rubber onto the floor like I suppose every student did, I had developed this craze to bury it into the little craters on the tabletop. I would press the residue hard using the end of a pencil or my bare fingers. Soon, I was busy producing residue for the sake of filling up the holes. It took a long time to fill up all the holes, large and small. When I was done with the job, I would start to dig out the residue from one random crater and fill it up with fresh residue. And the job never ended.
Unfortunately, there is no morale to this story. I think I should have studied to become a dentist instead.