There is none so blind as those who will not see, but those who are absolutely determined to see something will often do so, even when it's not there. Psychologists call it confirmation bias, and it manifests itself in almost any situation in which one truly wants to believe something: canals on Mars; the blatant off-sidedness of the goal against your team; the utter adorability of your children; the latest 'evidence' in support of your favourite conspiracy theory. If you're after evidence to bolster your existing beliefs, seek and ye shall almost certainly find!
Of course, the classic example of confirmation bias is the countless sightings of the Virgin Mary in pieces of toast, cappuccino foam, wood grain, and just about every other bizarre location you might care to mention. If such manifestations are indeed the Lord's work, then He really does move in mysterious ways. In reality, these 'sightings' are nothing more than vague, coincidental likenesses blown out of all proportion by people who have a very particular way of looking at the world.
In fairness to those who think they see the Virgin Mary in the stains on their bathroom wallpaper, the human mind is very much programmed to recognise facial features, so it's hardly surprising that we occasionally see faces when they're not really there. The British comedian Dave Gorman has an excellent set of photographs of 'faces' he has spotted in inanimate objects. There is also a Flickr Grilled Cheese Virgin photo pool.
Even us hoary, old sceptics aren't immune from recognising human faces where they are clearly not. In my own case, I have never spotted the Virgin Mary—well, OK, there was that one time in that pub in Wales—but, last month in Cambridge, I did clearly discern the face of none other than Charles Darwin in a cluster of brachiopods in the Sedgwick Museum:
What do you mean you don't see it? And you have the cheek to call yourself a Darwin groupie! The brachiopods do not lie!
It's the dawn of a new era!