So, I'm sure you ex-Catholics have heard this one: guy, circa 700 CE, witnesses a wafer turn into heart tissue and wine turn into five globs of blood.
A short 870 years later in 1574, the investigation gets underway. Supposedly, the miracle is proven, and it's now recognized by the Catholic church.
Now, the documentation for this, at least on Wikipedia, was sparse, especially concerning the results of the investigation. That aside, it does seem to me that the biggest hole in this story is the, y'know, 800-year gap between the event and the investigation. Seems like long enough for even the dumbest priest to fake something to show people.
I was surprised recently when someone brought this up, and noticed we didn't have an article on it. So, discuss away and we can throw a page together later.