Each of us visited the wonderful country called "Childhood". What is there just not befall us? Abrasions, bumps, cuts. In addition, probably everyone remembers what to eat as a child. In addition to "normal" food we ate coal, clay, sand, chalk, earth. How to remember - it becomes ridiculous. But childhood passes - habits remain. Many adults eat chalk. Just not the one that the teacher wrote on the board the task, and the edible chalk. Some of this shy and start to "complexes." The eating chalk there is nothing to worry about.