Few lines in "Heads Up" are as telling as the opening command, "Heads up, shoulders back." It sounds like advice on posture, but it also sounds like a voice the speaker has heard too many times, telling her how to hold herself. The poem is about the gap between looking confident and actually feeling it. Confidence, the speaker says, is "trapped inside the mirror," as if it lives in the reflection and not in the person looking at it.
The ballerina who twirls en pointe adds a picture of performing under watching eyes. The clapping "grows nearer," which could suggest approval, but here it feels more like pressure closing in. Then insecurity arrives, and the speaker claims society treats self-assurance as "a sin," so you are told to be confident and punished for it at once. The ending is quietly defeated: whatever the speaker says or does, the pressure wins. The mood is tense and self-conscious, with short, rhyming lines that feel almost like a nervous chant.