In rhetoric, they don't mean to be taken seriously and they don't understand when we do.
Thus an ultimatum is often not taken seriously and the reality comes as a surprise. Remember the "Mother of all Battles"? Like many other Mediterranean peoples, Arabs don't seem to mind making a scene in public and have a high blown sense of drama. Paul Harvey once described how he had spent the Suez Crisis hiding under the bed in his hotel room because of the blood-curdling radio broadcasts, before he learned that Arabs talk like that when they're arguing over a taxi. "This is my taxi and I will defend it to the death!" "You lie, it's mine and rivers of blood will flow in the street before I give up my taxi!"�
An Arab will scream at you, get into your personal space and sometimes kick dirt on your shoe -- and they react with utter surprise when an American up and decks him. "What did I do?" To say the least, this makes negotiations difficult.
It makes me wonder whether the nuclear saber-rattling in Iran is quite different from the nuclear saber-rattling going on in some Western cricles.