Board Thread:WARNING ALL USERS False Info\Spoilers/@comment-64.84.105.166-20130730041234/@comment-72.192.213.236-20130730042039

I'm relatively sure that would render the person witnessing the transformation (in this case, the Sheriff) frozen/in shock, unable to respond/understand. Thus disposing of their possible source of help. Also, Stiles probably did unrealistically think deep inside that his father would immediately understand, as he expected him to.