I'm impressed by the lengths to which the authors must go and have gone to refute the skeptics' counter-explanations. For example, they simulated the presence of a potentially observing competitor using an audio recording of a competitor that was not actually observing the raven caching its food. Indeed otherwise a skeptic might claim that the caching raven was acting as "observed" in response to the different sound, rather than (as the authors want to show) because it inferred that it can be seen when the peephole is open.
