Coup de Grace

As a full-round action, you can use a melee weapon to deliver a coup de grace to a helpless opponent. You automatically hit and score a critical hit. If the defender survives the damage, he must make a Fortitude save (DC 10 + attacker's base attack + melee damage attribute modifier + weapon's critical modifier) or die. Delivering a coup de grace provokes attacks of opportunity from threatening opponents. You can't deliver a coup de grace against a creature that is immune to critical hits.