On the prairie, those flint arrowheads can be found lodged in every sort of natural matrix: soil, sod, the mud of a riverbank, the heartwood of a tree. Waterhouse has a talent for finding them. How can he walk across a field salted, by the retreat of the last glacier, with countless stones, and pick out the arrowheads? Why can the human eye detect a tiny artificial form lost in nature’s torn and turbulent cosmos, a needle of data in a haystack of noise? It is a sudden, sparking connection between minds, he supposes. The arrowheads are human things broken loose from humanity, their organic parts perished, their mineral forms enduring—crystals of intention. It is not the form but the lethal intent that demands the attention of a selfish mind. It worked for young Waterhouse, hunting for arrowheads. It worked for the pilots of the airplanes that hounded U-553 this morning. It works for the listeners of the Beobachtung Dienst , who have trained their ears to hear what is being said by Churchill and FDR on what are supposed to be scrambled telephones. But it doesn’t work very well with crypto. That is too bad for everyone except the British and the Americans, who have devised mathematical systems for picking out arrowheads amid pebbles.