The movement of the fire truck is closely related to the movement of the lines in the poem. Williams produces a slow motion or "Doppler" effect (see "Sound Check" for more) by varying the lengths of the lines. The middle of the poem is where the lines are the shortest, and that's also where he describes the motion of the fire truck and the figure 5.
- Lines 1-13: The sound of the poem is onomatopoeic: it mimics one aspect of the sound of a fire truck moving past an observer. The lines get shorter toward the middle of the poem and then longer again at the end. For example, the shortest and most "tense" line in the poem is the word "tense."
- Line 7: Williams creates an ambiguity as to whether he is describing the movement of the fire truck, the figure, or both.
- Line 8: The word "tense" is a metonym that ascribes the tension of the situation – a loud emergency vehicle passing by – to the movement of the fire truck (and the figure). Neither a fire truck nor a number can actually be tense.