A Unique look into the Kimmel barn

[Storm Cadet]

Question, I've noticed many of his horses with a circular piece on their mouth bits (pix 6-9) what are they and why do some have them and some don't.

At Belmont last week I saw a horse in the paddock who I liked prerace, but in the paddock this horse had on 3 different appliances around his mouth and head and I threw him out. One of them was the circular patch. I've never had them on any horses I've owned in training or racing?

PS the horse ran like crap