Six short lines look at death on the road, and they refuse to be gentle about it. The speaker sets up a contrast: some animals get buried, with some care or ceremony, while others are left to rot on the highway. Even nature's usual cleanup doesn't happen. The vultures haven't taken the bodies and the worms haven't reached them. Instead, wheels keep running over what is left, indifferent to it.
The last line is the sharpest. "The shit—man or animal" suggests that, once a body is flattened on the road, it hardly matters which one it was. The title already asks the question, and the ending answers with disgust, or perhaps bitter irony. The speaker seems angry and numb at once, shocked by how casually life is discarded. The mood is cold and bleak. The poem hints that modern traffic and human indifference can strip dignity from any creature, including us.