The physics teacher, Howard Dax, dismissed the class. He picked up a felt-covered block and erased the diagrams he had drawn on the blackboard. He noticed with annoyance that the lines were shaky, and in one place was an irregular star where the chalk had broken because of his exasperation at his pupils—or more exactly, one particular pupil. When the blackboard was clean to the corners—Howard Dax was a very precise man—he turned around and saw that the particular pupil was still sitting at his d