Five short lines, and the first already sounds like a verdict. "This grave or prison, the heart" takes the most sentimental organ in poetry, the thing lovers are supposed to give away, and turns it into a place you can't leave. The word "this" points at the heart as if the speaker were standing inside it, tapping the wall. The little "or" is cleverer than it looks. The speaker can't decide whether the heart is a grave or a prison, and the difference matters. A prison has a sentence, and one day it ends. A grave has no such promise. Bonta leaves us with both possibilities, and the choice itself suggests how hopeless the speaker feels.
The next two lines turn that gloom into a question: "who could remember / what it was like to be released?" The verb is "remember," not "imagine." That quietly implies release did happen once and has been forgotten, so the loss is double: the freedom is gone, and so is the memory of it. "Released" carries several meanings at once. A prisoner is released on parole, a body from a grave is closer to resurrection, and a feeling can be released by being let out. Judging by the imagery, being shut inside the heart may mean being unable to let feeling out at all. The question mark is also telling. Nobody is expected to answer.
Then comes the shift. After the heavy metaphor, line four drops into the voice of someone mentioning an errand: "I went with a bottle or two." The vague "or two" is a casual shrug, almost comic after the grave and the prison. The poem never says what is in the bottles, so we supply it ourselves, probably wine or something stronger. Either way the bottles seem to do double duty, as a gift to bring to other people and as a way of loosening the speaker's own locked-up heart. Then comes the best word in the poem, "hunting." It is a predator's verb, and here the quarry is friends. The speaker doesn't visit friends or meet them; he goes out looking for them, which suggests they aren't simply waiting. The plural "friends" also hopes for more than one person. There is hunger in that last word, and a little embarrassment too.
The poem's construction supports this movement. There is no rhyme and no regular meter, but the ear still finds a pattern. Line one has about three beats, and the dash at its end holds the breath before the question runs on. The enjambment between "remember" and "what it was like" makes the sentence spill over the line break, much as memory slips. Notice, too, that the first line has no verb at all. It is a bare noun phrase, as static as the condition it describes. The first real action word, "went," doesn't arrive until line four, so the poem's grammar moves from stillness to motion at exactly the point where the speaker decides to leave the cell. The sounds shift with it, from the long, heavy vowels of "grave" and "released" to the clipped, practical consonants of "bottle," "two" and "hunting."
The title adds a final twist. "Prisoner" names the speaker, but a prisoner needs a jailer, and since the heart belongs to the speaker, the poem implies he is both. That makes the escape a matter of nerve and effort, not luck.
What makes the poem worth reading is how little it claims. It doesn't tell us the search succeeds. It ends with the speaker still on the way, as if the going itself were the answer. A big abstract despair is met with a small, human, slightly awkward action, and that mixture of dark metaphor and everyday errand rings true. Loneliness here is shown by what the speaker does, carrying a bottle or two into the world in the hope that someone will open the door.