Someone told me the other day about someone they’d heard about who had attempted to dry their pet poodle by putting it in the micro-wave oven with inevitably messy and tragic results. We marvel at the stupidity of a person who would do this as we pity the poor canine who suffered such an undignified demise. When I asked where they’d heard this they weren’t sure but they were certain it had really happened (and maybe it has)
An Urban Legend is a strange story that passes from person to person that usually has little basis in truth but is so darn exciting that we want to believe it. The actual person it happened to is usually removed by a couple of degrees of separation.
Some urban legends have been around for a long time, such as the one about alligators in the New York City sewer system. According to this one discarded pet alligators made their way to the sewers and grew to enormous size but were albino! Another famous urban legend states that a tooth can dissolve overnight if left in a glass of Coca Cola or that if you sneeze with your eyes open your eye balls will fly out-actually I think I believe that one.
We’ve all heard the story of the friend of a friend who awoke one morning to find her apartment covered in thousands of spiders, ostensibly because the cactus plant she brought home from Mexico was infested with spider eggs or the man who buys a kfc burger to find it’s really a rat, or the woman told by police not to get out of her car because the psychotic escaped patient is banging her (decapitated) boyfriend’s head on the car roof-Eeeek!
These and other urban legends pre-date the Internet and I’m sure even the printed word. by many years. Now they are spread via newspapers, gossip, and virally through the internet-like proverbially wild fire.
Photo and even video editing have enabled urban legends to enter the world of visual international media
It must be true because it elicited an emotional response from me!
Take a look at: What fuels urban legends
It is a kind of cognitive dissonance to think we are entirely rational whilst being overtly credulous but then again strange things really do happen. Ok maybe that one wasn’t true but how about this case of a man accidently badly injuring a woman and therefore saving her life even as she saves his at the same time! Come on life can be weird enough 
Urban legends are like negative jokes, but with a ‘punchline’ that induces the thrill of experiencing a negative emotion - fear, disgust, etc. instead of laughter.
Have you seen http://www.snopes.com/ ? It’s been around since 1995, and is popularly known as the definitive resource for urban legends - each legend is researched and given a ‘proved’, ‘disproved’, or ‘unknown’ status.