With the Mars Curiosity Rover roaming the surface of the Red Planet and sending us countless images to study, it was inevitable that unusual sightings and theories would start popping up.

So far, people have spotted a “man-made” pyramid on Mars and an eerie Martian woman overseeing the Rover's travels.

^{There was apparently a woman “watching” the Curiosity Rover as it took pictures of Mars. See the original image from NASA here.}

Also, it’s possible Mars may have crabs.

^{Supposed crab on Mars’ surface found by the Rover in late July 2015. See the original image from NASA here.}

Seeing images and faces in abstract scenes and landscapes is a surprisingly common occurrence – once you’re told as a child the moon has a “face,” you can’t unsee it no matter how hard you try. From the Virgin Mary’s face on a grilled cheese to an aggressive octopus coat hanger, we humans tend to “see” things that aren’t really there at all.

        

^{Left: Drunk octopus wants to fight. Right: A 10-year-old grilled cheese sandwich apparently bearing the face of the Virgin Mary was sold on eBay for a staggering $28,000. Can you see the Holy Mother?} 

So why does this happen? And so often?

As it turns out, there's a simple explanation for finding unexpected images in unusual places – the phenomena is called pareidolia. The word pareidolia is derived from the Greek words para, which means 'wrong' or 'instead of,' and eidōlon, which means 'image' or 'shape.' Pareidolia can be visual or auditory, the latter of which is believed to be the reason people think they can hear messages when they play certain songs backwards.

Pareidolia is basically defined as a psychological phenomenon that is triggered when we see an image or hear a sound, and the mind finds a familiar pattern or image within it where none exists. The easiest way to explain it is this: If you have ever laid outside with your friends seeing dragons, dolphins and other random images in the clouds – that’s pareidolia.

There are various theories as to why humans are plagued so acutely with pareidolia, but Carl Sagan’s theory is the most widely accepted. In his book "The Demon-Haunted World – Science as a Candle in the Dark," Sagan explains that the ability to identify threats in the distance or in poor visibility was imperative to our survival. Those early humans that saw what they thought to be a lion hiding in the shrub, ran away and as a result survived. Those without this ability, or who ignored potential danger, would have been eaten or killed. It's better to run away for no reason, than to not run away at all.

We therefore carry the genes of the people who ran away and were able to pass on the skill. While finding a pattern or image where it may not exist is a precautionary survival skill, Sagan commented that this could also result in the misinterpretation of random images or patterns of light as faces and familiar objects.

So although no one can say for certain whether there are crabs on Mars or whether Holy Spirits prefer to show themselves on toasties instead of incarnate – it's most likely just your brain finding familiarity in the unfamiliar.