When cast on a weapon, darkwound makes that weapon and instrument of great subtlety. Wounds caused by a weapon under the effects of darkwound are invisible and unfelt. Unless the character can physically see the wound being caused, he has no knowledge of its presence and considers himself physically fine until the spell duration ends. While wounds caused by a darkwound-enhanced weapon can be healed normally, they rarely are because of the difficulty in detecting them.
All damage suffered from darkwound is felt at once, at the end of the spell's duration. If the total amount of damage exceeds 50 hit points, the target must save against massive damage or die.