Final answer:
The simile "timidly as a mouse" illustrates that Eddie was feeling very shy when responding to the girl in the text "My Day at the Market".
Step-by-step explanation:
The author's inclusion of the simile "timidly as a mouse" in the text "My Day at the Market" to describe Eddie's response to the girl is meant to emphasize how shy or hesitant Eddie felt in that moment. When an author uses a simile likening a character's behavior to a mouse, it typically conveys a sense of shyness, meekness, or timidity, as mice are small and tend to avoid attention. Therefore, in this context, the simile suggests Eddie was feeling unsure and inhibited, rather than not answering, feeling like an animal, or literally being a mouse.