Cage muzzles may look fierce, but they are wonderful safety tools for a dog that is unpredictable in certain circumstances. They allow the dog to breathe normally, drink easily, and get food treats easily. They also allow the owner to relax!
Here is a post about cage muzzles that I recommend reading.
This weekend a new student's dog (recently neutered male, about 2 years old) was at my home with two other dogs. He seemed comfortable but as he was starting to interact with the other two dogs he suddenly and without provocation started to attack one of the dogs (an unneutered male). We broke it up quickly, but it surprised everyone, including the owner.
So we learned something about this dog-- at least in this highly-stimulating environment, he became so agitated that he became aggressive to another dog. Hmmm. A group class can be a highly stimulating environment, too, and