A duck walks into a general store and asks, "Excuse me but do you have duck food?"
The proprietor of the store says, "No. We don't carry duck food here."
The duck says, "Oh." and leaves.
The next day the duck returns and says, "Excuse me but do you have duck food?"
The owner says, "Didn't I see you yesterday? Like I said last time, we don't carry duck food here."
The duck says, "Oh." and leaves.
The next day the duck returns and says, "Do you have duck food?"
The owner, starting to get weary says, "Let me get this straight. We don't carry duck food - we never did and we never will, got it?"
The duck says, "Oh." and leaves.
The next day the duck returns and says, "Do you have ..."
The owner interrupts him and says. "Don't you dare ask about duck food this time! I've had it! If you ask me that one more time I swear I'm going to nail your flat feet to the wall!"
The duck says, "Oh" and leaves.
The next day the duck returns. "Do you have nails?"
"No."
"Do you have duck food?"