From a great distance, I thought I was seeing a black dog pawing the bark of this old tree. Upon closer inspection, I found that the animal in question was actually a flat piece of black metal shaped like a dog and adorned with a red painted collar. The illusion is so strong that even this photographic image may seem at first glance to show a “real dog,” at least until we see that the barking dog does not display the light on its back in the same manner the tree bark does. The play of light and shadow makes the tree seem three dimensional, while the dog presents itself in only two dimensions. The tree’s bark appears real, while the dog’s bark exists only in our imagination.