He asks him if he sells duck food
A duck waddles into a store and walks up to the shopkeeper.
“Do you sell duck food?” the duck asks.
“No,” says the shopkeeper.
The duck simply waddles away.
The next day, the duck comes back.
“Do you sell duck food?”
“No! I told you yesterday, we don’t sell duck food,” the shopkeeper replies.
The duck leaves again.
The following day, the duck returns and asks the same question.
The shopkeeper is getting frustrated.
“No! And if you come in here one more time asking for duck food, I’m going to staple your feet to the floor!”
The duck quietly waddles away.
The next day, the duck returns.
He walks up to the shopkeeper and asks:
“Do you sell staples?”
“No,” the puzzled shopkeeper replies.
The duck smiles.
“Great! Do you sell duck food?”