The ending in this story is pretty typical for a short story: a delicious, surprising twist. The wife and her husband seem to have reached the climax of their argument. She has all of these desires for a different life. He has no interest in hearing them. She has returned to her window and he has returned to his book.
But then…there's a knock at the door. The maid is standing there in the doorway with a cat in her arms, sent, as she says, by the padrone. Is it the same cat as the one the wife had seen in the rain from her window? That part remains unclear. Had the wife told the padrone what she was looking for a cat, or that she even wanted one to begin with? No and no.
This means that the padrone probably went through a bit of trouble to get this gift to the Americans' room. He must have first thought about the woman and decided he wanted to do something to help make her happy. He also would have had to talk with the maid, who did know what woman went out for. Then, of course, he needed to find a cat. It's a gesture of thoughtfulness—like when someone gives you exactly you want even though you never told them you wanted it. That's how the wife must feel at this moment. Hemingway, of course, doesn't tell us how she feels, but does he need to?