A man sees a sign outside a house - 'Talking Dog For Sale.' He rings the bell, the owner appears and tells him the dog can be viewed in the back garden.The man sees a very nice looking brown dog sitting there."Do you really talk?" he asks the dog."Yes," the dog replies.After recovering from the shock of hearing the dog talk, the man asks, "So, tell me your story." The dog looks up and says, "Well...I discovered that I could talk when I was pretty young. I wanted to help the government, so I told the SAS."In no time at all they had me jetting from country to country, sitting in rooms with spies and world leaders, because no one imagined that a dog would be eavesdropping."I was one of their most valuable spies for eight years. But the jetting around really tired me out, and I knew I wasn't getting any younger so I decided to settle down. I signed up for a job at Heathrow to do some undercover security work, wandering near suspicious characters and listening in. I uncovered some incredible dealings and was awarded several medals. I got married, had a few puppies, and now I've just retired."The man is amazed. He goes back into the house and asks the owner how much he wants for the dog."Ten quid," the owner says."10!!? But this dog is absolutely amazing! Why on earth are you selling him so cheaply?""Because he's a lying *******. He's never been out of the garden."