A duck walks into a pub and asks the bartender,
"Do you have duck food here?"
The bartender says no and the duck leaves.

The next day, the same thing happens. The duck wanders in and asks, "Do you have any duck food?" Once again, the bartender says no and the duck leaves.

On the third day, the duck enters the pub and the bartender asks, "What do you want this time?" The duck asks once more,
"Do you have any duck food?"
"No!" yells the bartender, "We don't have any duck food. If you come back and ask me again, I'll nail your feet to the floor!"

The duck leaves and comes back the next day and asks,
"Do you have any nails?" The bartender says, "No."
The duck then asks, "Do you have any duck food?"