A man brings a duck into a bar and asks the bartender, "Do you have any grapes?"
The bartender, confused, replies, "No, we don't sell grapes here, this is a bar."
Disappointed, the man leaves with his duck. The next day, he returns with the duck again and asks the bartender, "Do you have any grapes?"
The bartender, annoyed, says, "I told you yesterday, we don't have grapes! If you ask me again, I'll nail your beak to the bar!"
The man quickly leaves with his duck. The following day, he comes back with the duck once more and asks the bartender, "Do you have any nails?"
The bartender, surprised, says, "No, we don't have any nails here."
The man grins and asks, "Good. Then do you have any grapes?"