I now read the last comment from TRD, she was using a chain shank. To me that's even worse that the chain end of a lead line.
First off, I believe anything with shanks should have a non-jointed mouthpiece, or should have a mouthpiece that only allows very little movement.
Lunging with a shank is just crazy, you do not have the feel you have when you're on the horse holding the reins, and when lunging you pull the shanks to one side, which is very uncomfortable and confusing for the horse.

HUP HOLLAND HUP