A duck walks into a bar, and asks the bartender, "Do you have any grapes?"
The bartender says, "I'm sorry, Duck. We're a bar, and so we have wine and beer and mixed drinks. But no grapes." The duck is sad, and leaves the bar.
The next night, the duck comes back into the bar and asks, "Do you have any grapes?"
The bartender says, "No, Duck, I told you last night. We don't have any grapes! And if you come back in here tomorrow night asking for grapes, I will nail your beak to the bar!" The duck hops down off the bar and runs out the door.
The next night, the bartender is waiting for the duck to come back in, and sure enough, he does. The bartender grits his teeth as the duck asks, "Do you have a hammer?"
The bartender explodes. "What? No, of course I don't have a hammer!"
So the duck says, "Do you have any grapes?"