I understand that whatever instantly heals or harms player, it has the opposite effect on the undead. the arrow of harming is able to strike the undead and heal them (they can be shot at 10 arrows of harm II and will not die, as it should). the problem is when I shoot the arrow of healing II at an undead, the arrow bounces off them. the undead mob is damaged but the rate it takes to kill them is equivalent to that of a regular arrow. in fact the heal II arrow can be picked up again and keep the effect, a cheaper alternative to the infinity enchantment, for the undead of course. shoot 10 of heal II arrows on a creeper will not kill him, and the arrows are consumed. the harm II arrow instantly kills the creeper and consumes the arrow as well.