This whole process didn't start with me having the intent of looking for birds in rocks. No. Seeing birds and faces happened after quite a while. Now I can pick up a rock that I suspect is " different", turn it and turn it, slowly and look at at all the angles and suddenly perceive one or more images. It took a while to train my eyes to look for the subtleties and build this visual vocabulary. There are still a lot of details I don't understand, don't know what they are about. I just know they are " something". It is like any skill or focused obervation, it gets better, more skilled and acute.
This one looked like a big bird's head. The I found out under the beak, a tiny human profile!