In urgent need of a joke about protecting the environment

Customer: The rat poison you sell here doesn’t work at all! Not only did the mouse not die after eating it, but it also became fatter and fatter!

Shop clerk: Oh, that’s right. This is a newly launched green and environmentally friendly rat poison that does not contain any toxins. Its principle of killing rats is to fatten the rats. When the rats are so fat that they can't burrow into their holes, either cats or humans can easily kill them. Don't worry, just keep using it.