Rest... I need Rest...
I did get to look in the scope and see everything that was in there... so I suppose now I can say I know my horse inside out.
The verdict is that there is not, in fact, a caterpillar or a mouse or piece of wilderness stuck up my horse's nose. He just has a sinus infection, which means that he needs shots of antibiotics for a week.
The vet also floated his teeth, which means she used a giant electric drill with a file on it and filed down his teeth so that they would sit properly. He had to have a hideous halter put on his head to cover his teeth, keep him from biting, and hold his mouth open. It was awful and he hated it.
I suppose that Zydo and I are cut from the cloth in that we're both prone to sinus infections and we both hate the dentist. However, he was a total lightweight with the sedatives and that's something I plan to hold over him forever. Like, Look here, Buddy: You may weigh twelve hundred pounds and all BUT AT LEAST I CAN HANDLE A GOOD BENDER NOW AND THEN.