Again, the swallows represent a hopeful future, while the rats are indicative of corruption and greed. However, Marco implies that it’s very possible for there to be qualities of both swallows and of rats in one person, suggesting that this, too, is part of a cycle that takes place in the course of a single human lifetime just as it does in the wider arc of human history. It’s possible, in this sense, to see how humans can become different people as they take on more of one quality or another, just as cities change depending on how hopeful or corrupt they might be.