Knight and Hale made the call back in the 70's or early 80's I don't remember the name of the call but I wish I still had one. Most hunters would think they are hearing some kind of frog or loud bug. But in all actuality they are hearing a buck following a estrous doe or searching for an estrous doe. Only one person I have ever heard duplicate the call with their mouth and that is a lady. I will post the video if you want me too.