"Beat a dead horse" 是一句英语俚语，源自美国南部的马匹文化，字面上的意思是“鞭打一匹已经死去的马”。在比喻意义上，这个短语表示“反复讨论或强调一个已经毫无意义或明显的问题，或者试图让一个已经结束的讨论重新恢复活力”，通常带有负面含义，暗示这样做是徒劳无功的。

**例句**

1. "I know we've discussed this issue at length, but let's not beat a dead horse. We need to move on and focus on new strategies."（我知道我们已经详细讨论过这个问题了，但让我们不要老生常谈。我们需要向前看，专注于新的策略。）

2. "After the project was canceled, it was pointless to keep arguing about it; we were just beating a dead horse."（项目被取消后，再争论下去就毫无意义了，我们只是在做无用功。）

3. "When the teacher realized the class understood the concept, she tried to change the subject, saying, "Okay, let's not beat a dead horse here."（当老师意识到全班都理解了这个概念时，她试图换个话题，说：“好了，我们不要再在这个问题上纠缠不休了。”）

**同义词辨析**

1. **Reopen a closed door** - 这个短语意味着试图重新讨论或改变一个已经决定或结束的事情，与"beat a dead horse"类似，但更侧重于“重新开启”而不是“反复强调”。

   例句: "The case was already settled, so trying to reopen it would be like opening a closed door."

2. **Flog a dead horse** - 这是另一个与"beat a dead horse"非常相似的表达，也是指反复讨论一个没有结果或不再相关的话题。

   例句: "It's pointless to flog a dead horse; we should accept the decision and move on."

3. **Nail a jelly to a tree** - 这个短语形容尝试做一件极其困难或不可能完成的事情，虽然含义不同，但在某些情境下，如果一个话题被讨论得过于繁琐，以至于变得不可能有进展，可以视为与"beat a dead horse"有某种关联。

   例句: "Trying to convince him of that fact is like nailing jelly to a tree; he won't change his mind no matter how much you argue."

4. **Banging your head against a brick wall** - 此短语表示持续努力但无法取得进展，与"beat a dead horse"在某种程度上共享了徒劳无功的含义。

   例句: "I've been banging my head against a brick wall trying to get her to see reason, but she's stubborn as a mule."