Mrs. Abell "was very anxious" to have Lincoln stick to his promise.

But he wasn't.He admits he was "continually repenting the rashness"which had led him to make it,and dreaded the thought of marrying her as "an Irishman does the halter."

问题：an Irishman does the halter.是什么意思？有什么典故吗？为什么爱尔兰人会非常害怕缰绳呢？