A duck walks into a bar and asks, "Got any grapes?"
The bartender, confused, tells the duck no. The duck thanks him and leaves.
The next day, the duck returns and asks, "Got any grapes?"
Again, the bartender tells him, "No -- the bar does not serve grapes, has never served grapes and, furthermore, will never serve grapes." The duck thanks him and leaves.
Confused, the bartender says no.
"Good!" says the duck. "Got any grapes?"