The term Lourdes [loordz] effect was coined by Belgian philosopher and skeptic Etienne Vermeersch to describe the observation that supernatural powers never manifest themselves in a completely unambiguous fashion. According to Vermeersch, should the miraculous power of Lourdes actually exist there would be no reason to think that it would be more difficult for the Virgin Mary or God to reattach a severed arm than to cure paralysis or blindness.
The accounts and photos of, for instance, the Loch Ness Monster and the Yeti lack reliability and clarity due to a similar effect. Vermeersch uses this term to mock what he calls the selective and uncritical approach to miracles, or the frivolous attribution of supernatural gifts to human beings.
The Daily Omnivore 