Sherlock Holmes is known for approaching all mysteries with cool logic - and yet when his creator Sir Arthur Conan Doyle saw photographs taken by two young girls purporting to show real life fairies at play... he unwisely declared them genuine.

How did Elsie and Frances fool so many people with their photography... and why did they keep the hoax going for decades?

For a full list of sources go to timharford.com

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Playing board games and spending too much money are time-honored Christmas traditions, so to mark the festive season, Tim is joined by the creator of Magic: The Gathering - Richard Garfield - for a special Q&A about economics and game design.

How should you go about building the perfect game? Why did the Magic trading card market crash? Why do so many people hate Monopoly? Plus, Richard has a bone to pick with Tim about a previous episode of Cautionary Questions.

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A megaplant near the small village of Flixborough, England, is busy churning out a key ingredient of nylon 6, a material used in everything from stockings to toothbrushes to electronics. When a reactor vessel fails, the engineers improvise a quick-fix workaround, so the plant can keep up with demand. Before long, the temporary patch - a small, bent pipe - becomes a permanent part of the factory, and the people of Flixborough unknowingly drift towards disaster.

For a full list of sources, see www.timharford.com

See omnystudio.com/listener for privacy information.