Cats have theories. Every cat owner knows that. The cats can’t and won’t tell you their theories. You must deduce the theories from their behavior. Then you have theories about the cats’ theories. If you modify your behavior in response to your theories about their theories, you may change their theories. It is an endlessly recursive loop. The viewer affects the system. It’s Heisenberg’s uncertainty principle with cats.
Some of the Best from Tor.com: 2012 Edition - Patrick Nielsen Hayden, Liz Gorinsky, David G. Hartwell, Gene Wolfe

-from "About Fairies" by Pat Murphy
seen in Some of the Best from Tor.com: 2012 Edition