Final answer:
Without the correct context or reference to a character named Jo and her situation regarding the word 'dunk', it is not possible to provide a detailed answer to the question posed.
Step-by-step explanation:
The context of this question suggests that it relates to a character named Jo from a literary work. However, based on the snippets provided, we do not have a character named Jo or a situation involving the word 'dunk'.
It appears that there might be a mix-up with the names or the provided context is not related to the actual question about why Jo did not want the boys to know she hadn't heard the word 'dunk'. Therefore, without the correct context, it is not possible to answer this question accurately.