work of art that heighten the illusions

This is a great work of art which uses "Gestalt Principles" to heighten the illusion. At first glance, I saw a mermaid between the rocks. After several seconds, I found these two rocks are actually images of several persons. One of them is a king. However, if you look at the king for a while, he is actually made up with several little persons. More surprisingly, the mermaid disappeared after my careful observation. Her legs became water and her tail became white water. At that time, I realized that the rock on the left side has tree branches which made the illusion of a mermaid. The mermaid at the first glance is just our imagination.
This work of art uses the "Gestalt Principles" to heighten illusions. When we perceive shape and contour, we might have something that does not exist. This work of art is the phenomenon called "Subjective contours". This phenomenon, from our textbook, is the time when "our brains provide missing information about outlines."

This work of art also follows the "Gestalt Principles". We could see a face between the two horses when we first look at this picture. However, the nose and mouth of the face are rocks and a bird; the eyes and eyebrow are legs of the horses.
These work of arts are from Psychological arts: http://psycharts.com/illusions.htm
There is also a interesting video from YouTube that shows many work of arts that follow "Gestalt Principles" : http://www.youtube.com/watch?v=8aOSsafHalc&feature=related