They're called
Pareidolia
Pareidolia (/pærɨˈdoʊliə/ parr-i-doh-lee-ə) is a psychological phenomenon involving a vague and random stimulus (often an image or sound) being perceived as significant. Common examples include seeing images of animals or faces in clouds, the man in the moon or the Moon rabbit, and hearing hidden messages on records when played in reverse.
In his notebooks, Leonardo da Vinci wrote of pareidolia as a device for painters, writing "if you look at any walls spotted with various stains or with a mixture of different kinds of stones, if you are about to invent some scene you will be able to see in it a resemblance to various different landscapes adorned with mountains, rivers, rocks, trees, plains, wide valleys, and various groups of hills. You will also be able to see divers, combats and figures in quick movement, and strange expressions of faces, and outlandish costumes, and an infinite number of things which you can then reduce into separate and well conceived forms."
See....we're not going crazy after all. To find faces and object amungst other things is quite normal and people have been doing this for quite some time. Now, can you imagine cave women checking out there new caves and inspecting the walls first to find just the right image on the walls before they moved in? It could be why they started drawing on their walls. lol
Bryce Rabbit, just one of many findings at Bryce Canyon National Park. Do you see him in the middle laying on his back with his feet up?