A duck goes into a store and waddles up to the manager.
He asks him if he sells duck food. The shopkeeper tells him no. The duck then leaves.
The next day the duck returns and asks the same question again. The shopkeeper tells him, testily, that the store still doesn’t sell duck food. The duck leaves.
The following day the duck returns again and asks the same question. The shopkeeper is getting pissed off, so says no and warns the duck if he asks one more time, he will staple the duck’s feet to the floor.
The next day the duck goes back into the store. He waddles up to the (now red faced) shopkeeper and asks ‘Do you sell staples?’
'No'. The puzzled shopkeeper says.
'Great.' Says the duck. 'Do you sell duck food?’