NASA’s Mars rover Curiosity took a panoramic photo of the "Rocknest" site in September 2012, and eagle-eyed Scott C. Waring discovered the rodent and uploaded the image to the website UFO Sightings Daily, saying "NASA almost makes historical announcement, but chickens out."
"Note its lighter color upper and lower eyelids, its nose and cheek areas, its ear, its front leg and stomach. Looks similar to a squirrel camouflaged in the stones and sand by its colors," he wrote. "Hey, who doesn't love squirrels, right?"
But the rodent in question is really just a rock. Though there may be "habitable" pockets underground, the Martian surface would not support lizards and rodents, which people often "see" in images of the Red Planet.
Pareidolia is the name for the particular human quirk that makes us see faces and other familiar objects in random shapes, textures and surfaces. Seeing pirate ships in the clouds or the face of Jesus in a rust stain are both examples of pareidolia, as is the famous Face of Mars.
It's such a widespread phenomenon that designers at Berlin's Onformative developed Google Faces, which uses Google Maps and facial recognition software to find geographical structures on Earth's surface that are most likely to be perceived as looking looking like faces.