User blog comment:Abelskie/The Grimm-ness of Nick/@comment-1966944-20120215075932/@comment-1966944-20120215091807

It could also be that some creatures have the ability to identify a Grimm and some don't. The suspense is finding out who can or can't. But I agree that in taking that approach, it lets the writers be kind of lazy in that they don't have to explain everything or keep consistent in their set up of the mythology, which is frustrating to any serious and dedicated fans!