He reminded me that I had better not go to Po Toi Island today.
I shook my head.
他提醒我, 叫我今天最好不要到蒲台岛去. 我点头同意.
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   此句不能译作:......我摇头表示不同意. 这里的shook my head
表示nodded my head(点头同意)的意思, 这是因为英汉两种语言表达习惯不相同的缘故.
   也许读者会问:为什么要这样理解和翻译呢? 因为在I shook my head.
的上一句里有had betther not go这样的词, 而英语的回答和汉语不一样,
英语是针对事实而答的, 为了表示同意不去, 所以用shook my head.
   下面请看两个类例:
   1  Haven''t you taken my pen?
      你没拿我的笔吧?
      No, I haven''t.
      是的, 我没拿.

   2  It is not going to snow, is it?
      大概不会下雪吧, 你说呢?
      No, it isn''t going to snow.
      是的, 不会下.

   由此可见, 英语是针对事实回答, 汉语却是针对问题回答. 现再举两例, 以见一斑:
   The guards gesticulated that he had better not linger there. He shook his head.
   警卫人员作手势, 示意他不要在那儿逗留. 他点了点头.
   We must not lag behind the ogher soccer teams. said the team leader of Star.
   No, we mustn''t, they all shook their heads.
   我们决不能比其他的足球队落后啊, 星队队长说道.
   是的, 我们决不能落后, 他们都点点头.
   
   但请注意, 如果 I shook my head的前面没有表示否定涵义的词not,
则仍作我摇头表示不同意解. New Concept English第三册A Pound Too Dear
一课有这么一句:
   The man said that the pen was worth £10, but as a special favor,
he would let me have it for £8, I shook my head and held up
a finger indicating that I was willing to pa a pound.
   这里的shook my head就仍作摇头表示不同意解.