Lester has a cavity and they "remove" his tooth. They have a large tooth model with cavity in it to explain why a tooth is painful if it has a cavity, why a cavity is bad, and what a dentist does to repair the cavity.
He uses a cartoon clip to explain the anatomy of the nasal cavity and where mucus is produced. He then sets up a giant tube with nose hairs to show how the nose works. The hairs are meant to filter air before it goes into the body. Then he explains that snot and mucus trap bacteria and larger particles from going into the lungs. They blow feathers into one end of the "nose" and show that clean air is coming out the other end because the mucus trapped the feathers.