I used to have more than one big dog Tshirts. From the link above the idea is the dog naturally trains itself based on small cues of the sensation of mild choking.
This sensation is different/uncomfortable for them, and your dog will move back into position in order to make the feeling go away. -
Looking at the hyoid in humans and the stylohyoid and diagastric(posterior portion) muscles when they contract they elevate the hyoid closing off the glottis by the folding over of the epiglottis. Thinking of the dog's head what if the trainer was holding the leash tighter slightly on the left side of the dog's neck as compared to the right? Would there be a slight adjustment backward on the left side of the dog? I think I use the smaller muscles on my left under jaw in a tighter more undifferentiated way than I use the musculature on the right. I believe it is tied to how I communicate and what I see in others who are communicating to me. My tendency throughout my life was to pay no attention to this complex musculature region and say it had no influence on my posture and being. I no longer feel that this is the case.