"In the 13th century, young schoolboys learning to write filled these scraps with alphabets and short texts. Bark was ideal material for writing down things with such a short half-life. Then the pupils got bored and started to doodle, as kids do: crude drawings of individuals with big hands, as well as a figure with a raised sword standing next to a defeated beast (lower image). The last one was drawn by Onfim, who put his name next to the victorious warrior."
When I was in third grade, I liked to draw F-16s fighting giant robots, which I think is pretty much the same.