This is a short, deadpan story about a man who follows instructions so literally that he stops using his common sense. A college graduate takes a warehouse job filling orders. He's given a list of numbers and a cart, and told to pull items from the bins. When he reaches bin S. Y. 1300, he grabs what's inside, which turns out to be a dead rat, and he loads it on the cart like any other tool.
The humor comes from the flat, simple language. The sentences are short and plain, and they march along like the job itself. The word "proudly" is the funniest touch: he's pleased with his work and doesn't see the problem. The checker's scream is the only strong reaction in the poem.
The speaker doesn't show much feeling and just reports events. The mood is darkly comic, but there's a sharper edge too. The poem seems to poke at the idea that education doesn't guarantee sense, and at how a system can turn people into obedient, thoughtless parts.