Tolkien is notorius for treating inanimate objects like characters. Just look at the One Ring, in the book it has a presence and a force and its own will. The same applies to swords.

That's what I was thinking.
 

I mentioned above that Tolkien used the sword because something needed to be said, and there was no one there to say it. Like King stated, Tolkien used inanimate objects as characters sometimes. He used Gurthang in place of a character to make a point, that Turin deserved to die.