Okay, the user wants me to translate "dog-day" into Vietnamese. Let me check the rules again. The first rule says to translate all content into Vietnamese. The second rule states that if the content is already in Vietnamese, leave it as is. The third rule is to provide only the translation without any explanations.
So, "dog-day" is an English term. I need to translate it. The direct translation of "dog-day" in Vietnamese could be "ngày chó" or "ngày của chó." But I should consider if there's a common equivalent or if it's a specific term. However, since the user didn't provide context, I'll go with the literal translation. Let me confirm if "dog-day" is a known term in Vietnamese. It might not have a direct equivalent, so translating it as "ngày chó" is appropriate. I'll make sure not to add any explanations and just provide the translation.