New Yorkers can take city-run classes to learn how to make their homes and businesses less attractive to these guys. Ludovic Bertron/Flickr hide caption

itoggle caption Ludovic Bertron/Flickr

Rats aren't only problem in Tehran. These were running free over the weekend in Luton, England. Barcroft Media/Barcroft Media /Landov hide caption

itoggle caption Barcroft Media/Barcroft Media /Landov