Karen Bassey's poem puts us inside the head of someone who feels cut off from everyone around them. The opening lines set up a painful contrast: others smile while the speaker cries, and the heartbeat they listen to feels like the sound of dying. Whether that dying is literal or a way of describing emotional collapse, the poem doesn't say. After that, the speaker goes numb. Feeling, speech and hearing fade until only one sound is left.
That sound is hard to pin down. Other people dismiss it as "nothing," while the speaker's peers call it a "demon." The speaker both craves it and can't bear it, and it pushes them toward "unthinkable" acts. In the end it is named as loneliness, the only sound they have ever known. The final line, long and slow, describes something that listens but never answers. The mood is bleak, isolated and quietly desperate.