Oh - huh- I was wondering if the metal loop that hang down works like a psuedo curb strap, but having no leverage that didn't make sense. I suppose maybe it's used for leads? Like thoroughbreds have the loop IDK what it's called.
It's to keep the horse from opening its mouth too wide. When you lead a race horse, you put the pony strap right on the bit for the most control. It also keeps the bit from flipping in the horse's mouth.