While at her friend Carla’s house Jeannette discovers that Carla does not have pests or animals in her home, but the Walls’ house is full of stray cats and dogs, lizards, snakes, and other animals. She asks Carla’s mother how they keep their house animal free and she says that she uses a No-Pest Strip to keep critters out. When Jeannette tells her mother this, Rose Mary refuses to buy one, declaring that anything that kills animals probably isn’t healthy for them either.
Jeanette's mother refused to so much as kill a fly, citing that flies were nature's food for birds and lizzards, who were in turn, food for the cats..... that if you killed the flies, you killed the cats. In Rose Mary's eyes, the pests took care of themselves.