rodent bomb is a smoke bomb meant to kill rodents outdoors. They kill by smoking out burrowing rodents like rats or gophers. It is not a humane method of pest control (imagine the terror of slowly dying from toxic smoke inhalation).
If you're not convinced, then consider that it's not only cruel, but it's also ineffective.
With so many other types of humane pest control methods available, there's no need to use something as inhumane and ineffective as a rodent bomb. Much kinder methods can be used to remove rodents before preventive pest control is used to help stop them from returning. There are also several do-it-yourself tips on how to control rats in garden areas.