In this video, I work McIntosh in the bridle for the first time. Even though I kept the halter on at the same time, she really struggled in this session. I now mouth my horses through a different process, which you will be able to see in other training series.
Whenever a horse struggles, it is important to step back and determine what foundations and associations were missing to have made that experience a positive one. If going back to simpler questions and foundations doesn't resolve the issue, it is likely that the horse has a physical or chemical (such as grass issues or mineral imbalances) issue that needs to be addressed.