I finished untangling the massive snarl that became of a very expensive ball of yarn a couple of months ago.  ... I finished untangling it into one large ball and five very small ones, but never mind, it's not all one big twisty mess anymore.  And I have learned an important lesson, which is this:  it's not worth pulling silk/mohair from the center of the ball.  Use the outside of the ball as the working end, where you can get more yarn without committing friction.