Philip K. Dick, "How to Build a Universe That Doesn't Fall Apart Two Days Later" in The Shifting Realities of Philip K. Dick page 264

In my writing I got so interested in fakes that I finally came up with the concept of fake fakes. For example, in Disneyland there are fake birds worked by electric motors that emit caws and shrieks as you pass by them. Suppose some night all of us sneaked into the park with real birds and substituted them for the artificial ones. Imagine the horror the Disneyland officials would feel when they discovered the cruel hoax. Real birds! And perhaps someday even real hippos and lions. Consternation. The park being cunningly transformed from the unreal to the real, by sinister forces. For instance, suppose the Matterhorn turned into a genuine snow-covered mountain? What if the entire place, by a miracle of God's power and wisdom, was changed, in a moment, in the blink of an eye, into something incorruptible? They would have to close down.