This needs to be taken off the market NOW! It can cause pain, scarring, infection and injury for no reason. There are other, safer, devises to control your dog with.
Most people do not take the time to properly teach their dog how to lead and they think this is a quick fix. IT's NOT! If you don't use it right, like most people, then this is what could happen. Be patient with your dog and have compassion. All it takes is love, patience, and consistency. Thank you.