He has some grounding in physics and finds it implausible that, when a few hundred pounds of trinitrotoluene are set off in the neighborhood and the resulting shock wave propagates through a large pane of glass, the people on the other side of it will derive any benefit from an asterisk of paper tape. It is a superstitious gesture, like hexes on Pennsylvania Dutch farmhouses. The sight of it probably helps keep people’s minds focused on the war.