Merry's sword
...So passed the sword of the Barrow-downs, work of Westernesse. But glad would he have been to know its fate who wrought it slowly long ago in the North-kingdom when when the Dunedain were young, and cheif among their foes was the dread realm of Angmar and its sorcerer king. No other blade, not thought mightier hands had wielded it, would have dealt that foe a wound so bitter, cleaving the undead flesh, breaking the spell that knit his unseen sinews to his will.
It's irritating in a film to have holes that can be easily plugged. You wouldn't have to include the entire sequence. A simple off-hand comment by an elf or Gandalf along the lines of "Damn nice sword, Merry. I see by the consumer info label that it's one of them magic jobs designed to kill witch kings."