The speaker is hanging onto the rails of a rushing train, and the ride quickly becomes a picture of life itself. The train swings, thunders and clangs, and the speaker sways along with it. Then the poem shifts: time is the thing fleeing now, and life creaks and shudders like the carriage. Holding the rail becomes holding "the thread of life."
The mood is tense and increasingly bleak. The speaker imagines how easy death would be: just let go, and the body would be "flung, smacked and scattered." From there the self shrinks into "pieces of flesh and bones," a ragged doll sewn together. The final image is the hardest one. A child plays with the toy for a while, then throws it away when bored. The speaker seems to feel small, fragile and disposable, at the mercy of forces that don't care. The rhythm of the lines, with their paired verbs and repeated sounds, mimics the train's jolting motion and keeps the unease building.