It doesn’t take much to kill a man, truth be told. We are fragile creatures and if struck in specific places, we will bleed to death in a matter of seconds. And it doesn’t even have to be a powerful blow, mind you. Now, it's difficult to hit the mark during a fight – our enemy won’t make it easy for us. But this is why you train with your sword daily, to be able to make all your attacks count.
But what are the vital parts? First of all, wrists. If you are able to cut them, your opponent won’t necessarily die, but he will surely have a problem holding any weapon. And in the heat of battle, this often means that he shall soon be dead.