Some of the United States' biggest cities have resorted to using dry ice to kill rats. Since dry ice (frozen carbon dioxide) turns into a gas, sanitation officials simply need to drop chunks of it into rat infested burrows and let science do the rest. Longtime Slashdot reader mi writes: USA Today reports: "Earlier this week, USA TODAY observed Chicago sanitation department workers at one of the city's oldest parks scoop chunks of smoking dry ice into a burrow before quickly covering the entry and exit holes with dirt and newspaper to stop any rats from escaping as the -109.3-degree Fahrenheit gas dissipated. Sanitation workers say they treat burrows during morning hours, when rats are less active and most likely to be huddled inside the burrows. The asphyxiated dead rats then decompose in place and out-of-sight of city denizens who count the disease-carrying vermin among the vilest of indignities of urban living. 'We are seeing 60% fewer burrows in areas where we are using the dry ice,' said Charles Williams, Chicago's streets and sanitation commissioner. 'It's more environmentally friendly, and it's very humane on the rodents as well.'" Humane or not, what is so especially "undignified" about rats? What makes them worse, than, for example, cats, deer or wild horses?