A butterfly is usually the happy ending of a story about change: the caterpillar struggles inside its cocoon and emerges with wings. "butterfly" borrows that comforting story and then shows, line by line, why it doesn't fit. The poem describes a girl who hurts herself every night, apparently hoping the pain will release something trapped inside her. Its central idea is bleak and simple: the relief she is chasing never comes. The final words say it flatly: "the demons never / left."
The key phrase is "as if she were". The poem never says she is a butterfly, only that she acts as if she were one. The comparison becomes a story, either one she tells herself or one the poem holds up for inspection. It is tempting on purpose, with words like "beautiful" and "free" promising exactly what the act cannot deliver. The metaphor also breaks down under its own logic. A butterfly walks out of its cocoon and leaves it behind, an empty case. Here the cocoon is her own body, and she cannot step out of that. To escape she would have to tear herself open, which is what the poem shows, using a verb with nothing delicate in it: "tore open". Even the line break works against the pretty image. "cocoon" sits alone on its own line, small and sealed.
The form is free verse, with no rhyme, no capital letters and no punctuation until the very end. Without rhyme there is no chime to round things off or soften them. The lines are short and often stop mid-phrase ("trying to free / itself from its suffocating / cocoon"), which makes the reader strain forward, much as the girl strains against her cocoon. The whole poem is also a single sentence. Nothing pauses and nothing resolves, like the nightly cycle it describes. The only full stop comes after "left", the most hopeless word, so the poem ends with a door closing.
The imagery is small and physical. "tears mixing with her / pools of blood" joins two kinds of pain, one emotional and one bodily, in a single image. The plural "pools" suggests this has happened many times, and the possessive "her" makes the blood almost an ordinary belonging, something she is used to. Then comes "hollow skin". The poem has just said the demons are "trapped under" it, yet the skin is called hollow. Judging by the imagery, she feels empty and overfull at the same time, a lid with nothing in it that still holds something in. "Demons" is a familiar word, but its vagueness works in the poem's favour. We are never told what they are, so they stand for whatever torment a reader brings to them.
Repetition carries the argument. "every night" appears twice, once to open the ritual and once just before the demons are released. The phrase makes the act sound like a habit, and the habit is the evidence for the ending. If the release had worked even once, she wouldn't need to repeat it. The poem never states this. It lets the repetition make the point for it.
The poem matters because it refuses to romanticise. The butterfly image could make self-harm look like beauty or transformation, and the poem lets that image appear only to dismantle it, leaving the reader with blood, tears and failure. It doesn't explain why she hurts, offer advice or judge her. The third-person "she" keeps a careful distance, and nothing in the text tells us whether the girl is observed or the poet herself. Either way, the tone is quiet and unsentimental, and it takes her pain seriously as a cycle rather than a gesture. For a student reader it is also a lesson in how a metaphor can be tested until it fails, and how that failure can say more than the metaphor ever could.