The Girlfriend
In "Hum" Goldbarth is cuddling with his girlfriend. When a song comes on that reminds him of a previous lover, he gently urges his current girlfriend back to sleep. She is not responsible for his previous relationship, nor is she supposed to feel threatened by it. This is part of his life over which she has no control, so she drifts to sleep in his arms while he hums.
Monet
Monet is a visual impressionist, famous for painting flowers and garden scenes. His artwork is in the exhibit in Kansas City. In his observations from "After Seeing the Impressionist Group Exhibit in Kansas City, We Drive Back through Flatness to Wichita," Goldbarth notices the sharpness, the declarative nature of Monet's style and compares it to exclamation points.
Degas
In "After Seeing the Impressionist Group Exhibit in Kansas City, We Drive Back through Flatness to Wichita" Degas is another of the artists featured in the museum. He is famous for painting female dancers. Goldbarth views the curves Degas' subjects' arms and bodies like commas, continually promising something more.
A God
Goldbarth muses about the order of the universe as a manifestation of "A God." He supposes that God could be blind, reading the world in its many textures like a blind person traces braille with their finger. He understands God through the infinite complexity of everyday occurrences that people take for granted, like the multiplicitous nature of the wind -- at one time a breeze delicately tickling clothes hanging on a line and at another time a hurricane ripping through buildings. These ideas are found in the text of "Alveoli."