Joke

A duck walks into a post office and asks the man behind the counter: 'Do you have any corn?' 

The man answers politely: 'No, we don't have any corn here.' 

The next day, the duck enters again and asks: 'Do you have any corn?'

Annoyed, the man answers: 'No! We don't have any corn.' 

This goes on for a couple of days until finally, when the duck asks 'Do you have any corn?', the man gets so upset he yells: 'NO! For the last time we don't have any corn, and if you ask again I'll nail your beak to the counter!' 

The next day, the duck returns and asks: 'Do you have any nails?' 

The man answers: 'No.' 

Then the duck asks: 'Do you have any corn?'