Author William Faulkner foreshadows Homer Barron's fate in different sections of "A Rose for Emily."
... we knew that... she would have to cling to that which had robbed her, as people would.
The rat poison that Emily purchases is indeed for a rat, but not the rodent kind. I have to admit that the first time I read this story, I did not foresee the double surprise ending, and it provided me with a great sense of pleasure and satisfaction. I have taught the story many times, and new readers rarely are able to predict the ending; and even those who may have suspected that Emily used the rat poisoning to kill Homer NEVER could have predicted the aspects of the second pillow and the single "strand of iron-grey hair" that rested upon it.
Faulkner leaves Homer's fate to the readers' imaginations, but we can assume that Homer declined Emily's marriage wishes, so she decided to poison him. Instead of getting rid of the body, she kept it close to her, just as she had when her father died several years before. The "smell" that later permeated the house and surrounding property was Homer's stinking corpse; we can only wonder how soon Emily may have begun joining Homer's remains in the bed (and how she could live with the smell!). The second pillow in the bed with "the indentation of a head" was Emily's, and the iron-grey hair was hers as well. She had been sleeping (or at least reclining) alongside the corpse--probably since the night of Homer's death. It was a fitting conclusion for Miss Emily Grierson, a "fallen monument"--
... dear, inescapable, impervious, tranquil and perverse.