Six lines, three couplets, no capital letters and no punctuation: the poem looks like a thought that has been left half-said. Its central idea is how closely birth and death sit together. A birthday, the day we are meant to celebrate time, becomes the moment we are most aware of it running out. By the end the speaker is so fragile that even breath cannot hold together.
The title does a lot of quiet work. "Mortal coil" comes from Hamlet's speech about what happens when we "shuffle off this mortal coil", where "coil" means the fuss and turmoil of being alive. Modern ears hear something else too: a coil is a wound spring, the kind that drives a clock. That second meaning is my inference, but it fits, because a clock appears in the very first line. The title suggests a body and a mechanism at once, a life that is wound up and will run down.
That first couplet, "a clock to kiss / on my birthday", has no verb in the usual sense, only an infinitive. It reads like an item on a wish list or a label on a present. Kissing a clock is a strange gesture, tender and a little absurd. It could be affection for the thing that measures us, or a farewell. The poem leaves it open, and the open question is part of its unease. A birthday ought to be a gift, but this one arrives with a timepiece.
The leap into the second couplet is abrupt. Nothing connects the birthday to "buried in this coffin", and the white space between them does the connecting. Even the sounds link them: "birthday" and "buried" both begin with that soft, closed *b*, so the two ends of a life are set side by side. The word "this" matters too. The speaker does not say "a coffin" but "this coffin", pointing at it as if we were standing inside with them. Then comes the odd company: "with an echo". An echo needs hollow space, so the word tells us how empty and enclosed the box is. It is also a sound that has outlived its source, a voice, or perhaps a tick, repeated after the original has gone. The only companion the speaker has is a leftover.
The final couplet turns on "but", though it never says what is thin. It could be the echo, the air, the wood, or the speaker themselves. Because the poem withholds the noun, the thinness spreads over everything. Then comes "the very breath broke". Breath does not normally break. Glass breaks, and so do threads and voices. Making breath brittle turns the most basic sign of being alive into something that can snap. "Very" adds pressure, as if even the last, most essential thing is giving way. It is also worth noticing that "broke" is the only finished, past-tense verb in the poem. Everything before it hangs in suspension, with "to kiss" and "buried" describing states rather than actions. The one completed event is a breaking.
The sound of the poem supports this. There is no rhyme, so nothing cushions the reader. Instead there are clusters of hard *k* sounds in "clock", "kiss", "coffin" and "echo", and small, tight short *i* sounds in "kiss", "in", "this" and "thin", which feel narrow and pinched. The lines are short, from three to six syllables, and the shortest, "but so thin", is the one that describes thinness. The poem ends on "breath broke", where the *b* returns from "birthday" and "buried" and the final *k* stops the mouth. If you read it aloud, you have to cut off your own breath to say the last words, which means the poem happens to you as well as to the speaker.
What makes the poem worth reading is how little it explains. It never says "I am afraid of dying," and it does not need to. A kiss, a coffin, an echo and a snapped breath are enough to make the reader feel the idea. It also shows how much a small poem can leave to its readers, who have to decide what the clock means, what is thin, and who is lying in the box.