When Billy is settling into the bed and breakfast and getting to know the landlady, he starts to take note of the strange things she says and does. As he starts to theorize about the source of her unpredictability, he alludes to World War II, as seen in the following passage:
Now, the fact that his landlady appeared to be slightly off her rocker didn’t worry Billy in the least. After all, she not only was harmless—there was no question about that—but she was also quite obviously a kind and generous soul. He guessed that she had probably lost a son in the war, or something like that, and had never gotten over it.
Here Billy guesses that the reason the landlady is “off her rocker” is because she “had probably lost a son in the war, or something like that, and had never gotten over it.” Dahl wrote this story in the years after World War II and would have expected his readers to understand that he is referencing the effects the war had on the mothers of young men who died in action. Billy interprets the landlady’s interest in his body and his youthfulness as the longing of a mother for her deceased son, not realizing that she is actually wanting to kill him and add him to her collection of stuffed young men.