The poem's frequent sibilance adds to its tense and disturbing atmosphere. It is often linked to descriptions of the cold and wind. For instance, take the first line: "merciless iced east winds that knive us." The intensity of /s/ sounds evokes the sound of the winds hissing by the soldiers.
In line 4, the poem uses sibilance to create a sense of hushed tension: "silence, sentries whisper, curious nervous." Here, sibilance reflects the sound of whispering voices and heightens the feeling of anticipation that the soldiers feel.
Another striking moment of sibilance comes in line 16: "Sudden successive flights of bullets streak the silence." As with the poem's first line, the intensity of /s/ sounds here mirrors the whooshing sound of the bullets "streaking" through the night air.
Throughout the poem relies not only on /s/ sounds, but also /sh/ and /z/ sounds—which, in many definitions, are also considered sibilant. Take lines 23-34, where the combination of /s/ and /z/ sounds reflect the lolling, dreamy quality of the line as the soldiers drift in and out of consciousness:
and stare, snow-dazed,
Deep into grassier ditches. So we drowse, sun-dozed,
Overall, the poem's intense sibilance makes it feel as if the snow and wind are swirling around the lines themselves. For the reader these sounds are inescapable, just as the weather they often describe is inescapable for the soldiers.