The wall is bumpy rock, not paper. You have no pencils, no paint box, no rainbow of colors. You have red and yellow dirt you can grind, black from burned wood, a little fat or water to mix, a hollow bone, and a sharp stone that can scratch. If those are your only tools, what kind of picture could you actually make, and what would be impossible? Would you smear color, blow pigment around your hand, or carve a groove?