Nasruddin was eating some walnuts, shells and all.
"What on earth are you doing?" asked his wife, surprised. "Why don't you crack the shell and take the nut out before you eat them?"
"Well," said Nasruddin. "I already know there's a walnut in there, so I don't need to crack the shells in order to find that out."
He then ate another walnut in the shell.
"Plus, when I paid for these, I paid by the pound, shells and all. If I throw away the shells, that's like throwing away money!" Nasruddin explained. "This way, I'm getting my money's worth."
Inspired by: Mulla's Donkey and Other Friends by Mehdi Nakosteen
Notes: This story is on p. 99 of the book. Nakosteen's version only has the part about not needing to open the walnut to see what's inside, but I read the part about buying-things-by-the-pound in another Nasruddin story, so I included that here. Compare the fairy-tale motif of the boy who is ordered by the king to bring him something no one has ever seen before; the boy brings him a walnut, and the king protests that he has seen walnuts before, but then the boy cracks open the nut in front of the king and says, "But you have never seen THIS walnut!"