An apparently simple question can cause great confusion. An American colleague of mine used to greet me every morning with question 'what's up?' to which I would reply 'Nothing' or 'I'm fine.' After the third time it occurred that for her the question was an all purpose greeting whereas to British ears it meant 'what is the problem?' or 'is something wrong?'.
The American usage is gradually taking over but the confusion remains - more interesting thoughts on this here
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