I recently had a player attempt to make a called shot against an monster's head. If I remeber correctly the rule for called shot only discuss leg (- to movement) and arm (- to attack). I told the PC that the attack had a -10 (guess???). He attempted the shot any ways. I was luck he missed, but if he would have hit is it considered an instant Kill? Or how would i assess damage??
One of the few thing you don't want to hear while deer hunting with your brother-in-law "DUCK"
It would have had no effect (aside from the usual hit point loss) unless you are using some sort of hit location house rules. The current rules system makes no differentiation in where you hit your oponent.