Well, after all the discussions so far, I just would like to add on ething here. The 'r' is not pronounced for certain when it is in the 'end' of a word and certainly not when it is in the middle of a word and follows a vowel. So, the word 'world' is pronounced as 'wold'. Similarly, some more examples, 'heard' ,'curl'. In words 'butter', matter', the 'r' is not pronounced. And whenever there is a word with a double 't' as in the above two words 'butter' and 'matter', it is always pronounced as 'd'.All this in the grammatically correct British English( no offence meant to others). Well, in America, you can talk as you like and get away with it.