Bob is standing in the park with a dog, John comes over with his son and asks if he can show his son the dog.
Bob “no problem”
John “Does your dog bite”
Bob “No, never bitten anybody in his life, he is so friendly and great with kids”
John puts his hand in front of the dog and it gets bitten clean off his arm, he screams “I thought your dog didn’t bite”!
Bob says “that’s not my dog……” 
