嘴巴里的词？好像没有这种说法。

但是你要仔细想想，这也没错，因为by word of mouth就是通过口头来传播。也就是一个消息经过一传十，十传百以后，许许多多人都知道了这件事。

举个例子：

I think the best form of advertising is by word of mouth. People don't believe a lot of what they hear or see in paid-for advertisements, but when they hear a recommendation directly from a friend, they are far more likely to act on it.

我认为最好的广告方式是口口相传。人们不太相信他们听到的或看到的那种付钱做的广告。当他们直接从朋友那儿听到推荐，他们就很可能会采纳。