Stephen Dubner

That is Bobby Corrigan. He is an urban rodentologist, a former rodent researcher who now works for the city of New York.

That is Bobby Corrigan. He is an urban rodentologist, a former rodent researcher who now works for the city of New York.

It is a cold and windy afternoon in lower Manhattan, one of the oldest parts of the city. Most of the humans have scurried back to their offices from lunch. At the intersection of Murray and Church Streets, Corrigan points to a sidewalk curb that has collapsed in on itself.

It is a cold and windy afternoon in lower Manhattan, one of the oldest parts of the city. Most of the humans have scurried back to their offices from lunch. At the intersection of Murray and Church Streets, Corrigan points to a sidewalk curb that has collapsed in on itself.

It is a cold and windy afternoon in lower Manhattan, one of the oldest parts of the city. Most of the humans have scurried back to their offices from lunch. At the intersection of Murray and Church Streets, Corrigan points to a sidewalk curb that has collapsed in on itself.

And where did these burrowing rats come from?

And where did these burrowing rats come from?

And where did these burrowing rats come from?

So you've got rats in the sewers, rats burrowing under the sidewalks. What else can we see?

So you've got rats in the sewers, rats burrowing under the sidewalks. What else can we see?

So you've got rats in the sewers, rats burrowing under the sidewalks. What else can we see?

Bobby Corrigan, as you can tell, is something of an enthusiast when it comes to rats. Although his enthusiasm is a strange blend of appreciator and exterminator.

Bobby Corrigan, as you can tell, is something of an enthusiast when it comes to rats. Although his enthusiasm is a strange blend of appreciator and exterminator.

Bobby Corrigan, as you can tell, is something of an enthusiast when it comes to rats. Although his enthusiasm is a strange blend of appreciator and exterminator.

He acknowledges that his work has its disadvantages.

He acknowledges that his work has its disadvantages.

He acknowledges that his work has its disadvantages.

When you walk around these old city streets with Corrigan, it's easy to feel that it's a rat's world and we're just living in it. As we learned last week in part one of this series, New York and other cities are struggling to control their rat populations. The problem here got so bad that the city declared war on rats. Today on Freakonomics Radio, how do you execute such a war?

When you walk around these old city streets with Corrigan, it's easy to feel that it's a rat's world and we're just living in it. As we learned last week in part one of this series, New York and other cities are struggling to control their rat populations. The problem here got so bad that the city declared war on rats. Today on Freakonomics Radio, how do you execute such a war?

When you walk around these old city streets with Corrigan, it's easy to feel that it's a rat's world and we're just living in it. As we learned last week in part one of this series, New York and other cities are struggling to control their rat populations. The problem here got so bad that the city declared war on rats. Today on Freakonomics Radio, how do you execute such a war?