A rabbit lives its whole life in silence, and the poem is about the single moment that silence breaks. The speaker describes its death in flat, quiet detail: the scream, the kicking legs, the dislocation. The word "final act" makes it sound almost theatrical, as if the rabbit has been saving everything for one terrible performance. The speaker doesn't say "I feel sad" or "this is cruel." The feeling comes through in how carefully and calmly the scene is laid out.
The title helps. "History of Screams, No. 5" suggests a series, so the rabbit's scream seems to be one example among many, a record of suffering that usually goes unheard. The last line, set apart from the rest, is the quietest and maybe the most unsettling: "then there is just the quivering." The noise is over, but the body hasn't quite stopped. The mood is hushed, stark and uncomfortable, with a sadness that sits in the stillness rather than in the scream itself.