At the beginning of World War I, the uniform of the British soldiers included a brown cloth cap. As the war went on, the British officials became more and more concerned about the growing number of soldiers suffering from head injuries. They decided to replace the cloth cap with a metal helmet. However, to their surprise, the number of soldiers with head injuries grew even more, although the intensity of the battles was the same before and after the change. So why did the number of head injuries per battalion increase even though all the soldiers were wearing metal helmets instead of cloth caps?