In my opinion, with this sentence Gruen is trying to propose that whenever animals are able to do something that only humans can do, it is not taken seriously and receives a lot of skepticism. Skeptics want to maintain the human exceptionalism no matter what and scientists who work with animal behavior pose a threat to their principles. This makes it tough for scientists to prove animal capabilities because skeptics continuously deny or diminish everything that puts animals closer to humans. The worst part of this, I believe, is that skepticism usually wins simply because of the conventional belief of most humans that all animals are inferior to
