Twinning: As a swift action, the wielder of a twinning weapon can command it to create a copy of itself in the wielder's free hand. To use this ability, the user must be wielding the weapon normally, and must have enough hands available to wield the copy. Only one copy can be in existance at a time.
The copy is treated as an exact duplicate of the weapon in all ways, including magical properties, except for the twinning ability itself. Only the original weapon can create copies.
If a copy leaves the wielder's hand for any reason, it vanishes at the end of the current turn.