Nightjohn has recently returned, after three nights away, much to Sarny's delight. His presence in Sarny's life is as welcome as ever, especially given all the problems she's had in her life recently.
Nightjohn takes her to a makeshift school he's set up in a ditch by the river where he teaches slaves how to read. By the light of three pitch torches, Nightjohn uses a catalog as a teaching aid, an aid that contains pictures of all the wonderful things you can have if you've got money but that slaves are not allowed to have.
Nightjohn's sure that Sarny is familiar with some of the pictures in the catalog and wants her to help him in his lesson by identifying them. Sure enough, she recognizes lots of them, pictures of dresses and shoes with buttons and little gloves and pretty hats and overalls. Sarny starts to cry at all these lovely things that she and other slaves don't have and never will have so long as they remain in their present condition.
However, Sarny's mood soon changes to one of excitement when she sees a picture of a horse. She's excited because beneath the picture is the word BAG, and this was the very first word that Sarny learned how to spell.