Have you ever caught a glimpse of something out of your eye and thought, "oh that looked like a face!" "Look, Jesus is in my bar of soap!" "That cloud looks like a dog running!" That's pareidolia. You see something random and your mind fills in the blanks so that you think something is there.
Pareidolia: a psychological phenomenon involving a vague and random stimulus (often an image or sound) being perceived as significant.
In psychology, the Rorschach test is a series of images used to invoke pareidolia to delve into the psyche of the patient. In religion and superstition, a vague stimulus is believed to be divinely sent. Here is a news story of Mary in bird shit. Notice how the people react to a random stimulus.
No matter how much I look at this picture, it looks like a face. The sink looks a bit shocked or frightened.
Carl Sagan hypothesized that detecting faces is a hard wired evolutionary advantage. This allows people to use only minimal details to recognize faces from a distance and in poor visibility but can also lead them to interpret random images or patterns of light and shade as being faces.
In 2009 a study was done to show that objects incidentally perceived as faces evoke an early (165 ms) activation in the ventral fusiform cortex, at a time and location similar to that evoked by faces, whereas other common objects do not evoke such activation. This activation is similar to a slightly earlier peak at 130 ms seen for images of real faces. The authors suggest that face perception evoked by face-like objects is a relatively early process, and not a late cognitive reinterpretation phenomenon.
Which would explain why everyone sees the following simple line drawing as a face:
This one, is of course, totally real. The Flying Spaghetti Monster is a holy visage mighty to behold! May you be touched by his Noodly Appendage!
Here's a strange 6-legged sky pig.
This is the famous grilled cheese toast image. If you ask me, the face in there looks more like an actress from the 40's than a religious icon.
And one more, for fun.
So, it's nothing supernatural. It's just the way our brains work to fill in information and make sense of the world as fast as we can.