Festus has a toothache. Coincidentally, for this episode only, Doc's office is set up with a chair for dental patients, and a table with some dental tools and sponges to absorb blood. The cot that is usually in the office is not there.
Each time Dr. Schultz addresses Doc Adams by his first name - Galen - Matt, Kitty and Festus each seem surprised to hear the name. After all these years, especially for Matt and Kitty, it's strange that they wouldn't know Doc's first name.