What does Waller do to Mammy in Chapter 5 of Nightjohn?
In Chapter 5, Waller chains Mammy up, whips her clothes off her, forces her to wear a horse harness, and subsequently whips her until her back is raw.
As the chapter begins, Sarny talks about the excitement of learning her letters and numbers from John, another slave. The young girl is so happy to learn that she scratches out her first word ('bag') on every piece of dirt she can find. Eventually, the plantation owner, Waller, catches her in the act of writing.
Waller is furious and proceeds to physically attack Sarny, who just manages to get away from him. Sarny runs to Mammy in fear. Eventually, Waller catches up to Sarny and demands to know the identity of the person who has been teaching Sarny how to read and write. Mammy doesn't give him a name, and Waller soon turns his fury on her. He has her shackled to the walls of the spring house and leaves her there in great pain for most of the day. When he does finally emerge from the house, he demands an answer to his original question, but Mammy still remains stubborn. At that, Waller tears her from her chains, rips her clothes off her, and orders her to put the horse harness around her neck. He then proceeds to whip her back mercilessly while she desperately tries to pull the buggy he is on. Due to his sadistic nature, Waller also makes all the field slaves witness Mammy's humiliation.
Unable to bear it any longer, John finally speaks up and admits to teaching Sarny how to read and write. Upon hearing that, Waller has both of John's middle toes hacked off with a chisel and hammer. Chapter 5 ends with Sarny wishing the worse kind of hell there is on Waller.