Seeley Swan Pathfinder -

A parent looking at a child's poor report card might say, "You'd better keep your nose to the grindstone next semester and get those grades up!" Is this parent suggesting painful disfigurement will make the child smarter? No, the parent simply wants the child to focus more time, effort and attention on school studies. But how do the nose and grindstone enter in?

One theory relates to the milling process. In an earlier age, grains were transformed into flour by using two large millstones, one fixed and the other turning. Grains between them were ground into powder. If the millstone overheats...