Thinking of the old KitKat advert where the person neatly slices down the centre of the bar (to ruled accuracy) with their thumbnail, and every other chocolate bar advert where the top of the bar is ripped off in a perfect neat way despite being against the grain of the glued folds or whatever.

It's quite annoying as I can't do this and I feel mis-lead. Is there a knack to this or is it just cynical advertising involving the packaging being pre-scored in such a way to enable unfeasible opening?