Nettle's poem sets life and death side by side as two opposing forces working inside the speaker's own body. In the first half, life fills everything: it pulses through the veins, blows through the lungs, and fills the stomach. The second half repeats those same images, but flipped. Death clots the veins, deflates the lungs, and empties the stomach. The matching structure makes the shift feel stark, as if one force is simply reversing the other.
The final lines change the perspective. The speaker steps back and watches their life as a butterfly with "paper-thin wings," something beautiful and easily damaged. Death's "icy grasp" freezes it in place, so it is stopped rather than destroyed outright. The mood is quiet, eerie, and helpless. The speaker doesn't struggle or protest, only observes, and that detached watching makes the loss feel even more chilling. The poem suggests how fragile life is, and how a living thing can be held still in a single moment.