Most humans, it seems, still put up fences around their acts and thoughts – even when these are piles of shit – for they have no other way of delimiting them. Contrast Paleolithic cave paintings, in which animals and magical markings are overlayed with no differentiation or sense of framing. But when some of us have worked in natural settings, say in a meadow, woods, or mountain range, our cultural training has been so deeply ingrained that we have simply carried a mental rectangle with us to drop around whatever we were doing. This made us feel at home. (Even aerial navigation is plotted geometrically, thus giving the air a "shape".)