This duck goes into a bar and asks the barman 'Have you got any bread?'.
'I'm afraid not' he replies, and the duck goes and sits down

A few minutes later the duck comes to the bar again. 'Have you got any bread?'
The barman says 'No I haven't, I just told you that' and the duck returns dejectedly to its seat.

A few minutes later and the duck's back. 'Have you got any bread?'.
'No I bloody haven't,' says the barman, 'and if you ask me again I'll nail your bloody bill to the bar'.  The duck, looking even more glum, waddles back to its seat.

Another couple of minutes and it's back. 'Have you got any nails?'
'No I haven't' snaps the barman.
'Have you got any bread then?'