Trench warfare during World War 1 involved deep trenches protected by barbed wire and machine guns that were used for shelter and movement between positions; chemical weapons like chlorine gas destroyed victims' respiratory systems while mustard gas caused blistering, bleeding, and vomiting with painful effects on the lungs that often led to strapped immobilization and death over several weeks; trench foot was a condition caused by prolonged exposure to cold, wet conditions without removing soaked boots or socks that could result in numbness, infection, and gangrene requiring amputation; estimates of total deaths during the war range from 8.5 to 12 million men with descriptions of mass graves noting detached and maggot-covered bodies that had the texture of soft cheese due to decomposition.