Some walls are stronger than others. Try to break through a wall built with straw and you are met with very little resistance. Try to break through sticks and the effort required is greater. Encounter a wall built with layers of bricks and you will then realize that some walls are really stronger than others. Each layer bonded with the other layer adds more resistance and toughness; until a nearly impenetrable wall as wide as it is thick is created and built to last. The human body has a...


