Nehemiah Trot, the poet, from the tumbled northwestern side of the graveyard, had begun to declaim his thoughts on the matter, although what they were no person listening could have said, when something happened; something to silence each opinionated mouth, something unprecedented in the history of that graveyard.

加粗部分是让步状语从句，修饰前面的had begun to declaim his thoughts on the matter。这个从句的特殊之处是采用了宾语前置。从句的主语是no people. listening为现在分词作后置定语，could have said是从句的谓语，what they were是前置的宾语从句。they指代前面提到的his thoughts. 通过宾语前置的手段，复数人称代词they的指代就越过了复数名词people，读者就很容易将they和thoughts联系起来。换句话说，指代和前置这两个修辞手法加强了从句内容和主句内容之间的联系，同时也避免了误解they的指代对象的可能。

从句译文：虽然倾听的人中没人能说出他的那些想法究竟是什么。