I've never heard of that way of slaughtering chickens, when it comes to me i make sure they havent eaten all day and when it comes to the killing point they're upside down in a cone. just putting them upside down calms them and i use a very VERY sharp blade and and slit their throat just under where you can feel their jaw, they only feel the part were you cut through the skin and after that there always dead right after the start bleeding