 Director Lamberto Bava stated in an interview that the story came to  him while he was reading a newspaper in which an article told how,  in American National parks, the game wardens were worse than the  poachers and were selling off the animals. As he then went to  America to shoot the movie, he realized that these parks were made  more for men than animals; nobody could care less about the  creatures! Though no animals were hurt deliberately during the  production of the movie 