It's the pebble song that teaches how to build a wall ... And when a pebble doesn't feel well in a wall, the wall doesn't stand right.  I am always fascinated by walls, their presence in human society and its impact on environment. By its silence, a wall reveals many truths about the way we lived our lives and about our sedentary lifestyle. The more we observe and analyze, the better we understand that there are a real complex relationship between humanity and nature.