"Demonstratory" is a word in ENGLISH

It was well known that a certain lake was very poor for fishing up north, but a game warden happened to notice that one guy kept coming home with his limit of fish on several occations. He asked the guy: "How is it that you are catching fish out of that lake when no one else can?" The guy replied: "Well I am going back up there tommorow, why don't you come along?" And, so the warden did. They were in the boat when the fisherman reached over and lit a stick of dynamite and then tossed it overboard. BOOM!!! There were fish floating to the surface all over! The game warden freaked out, and said: "You can't do that! That's illeagal!" The fisherman reached over and lit another stick and said: "Are you going to fish, or talk?"