Joe is looking for a new dog, and passes a house in his own neighborhood with a sign in front: Talking Dog for Sale.
So he stops and rings the doorbell. "The dog's in the backyard," his neighbor informs him.
Joe goes around back and sees a golden retriever in the yard and asks, "Can you really talk?"
"Yep," the dog answers.
"So, what's the story?" Joe continues.
"Well, I discovered I could talk when I was just a puppy," the dog began. "I decided I wanted to help the government, so I went to the CIA and demonstrated my skills. Soon they had me jetting from nation to nation, sitting in rooms with politicians and military leaders, since they logically figured no one would suspect a dog of eavesdropping. For eight years I was their most valuable spy.
"But I wasn't getting any younger, so decided I needed a settled job, and this time I went to the airport and volunteered to listen in on suspicious characters' conversations. I was spectacularly successful at this, too, and was awarded a bunch of medals.
"More time passed and I retired, got married, had a bunch of litters of puppies, and here I am now."
Amazed at this narrative, Joe runs up to the front door and asks his neighbor how much he wants for the dog.
"Ten bucks!" Joe exclaimed. "Holy Cow! That dog is truly amazing! Why just ten bucks?"
"Because that dog is a big fat liar. He never did any of that stuff."