The usage of sibilance illustrates nature as an enemy. The sibilant consonants resemble the sound of ammunition, indicating to the reader that the real threat is snowflakes, which pierce through the air akin to bullets. This breaks the preceding solitude. It indicates that the soldiers' anticipated struggle is with nature rather than the opposition. The snowfall is not the "dull rumour of some other war," but a genuine threat. The perilous aura is reinforced by the serpent-like overtones of the sibilance used.