The question is from the book "I know why the cages birds sings". Momma has two vital rules which are that one should not be impudent and dirty.
Momma "keep her cool” so well when she is being “aped” by the "powhitetrash” girls as she believed that the girls were not worth her time and due to this, she was calm and wasn't bothered.
Momma continued humming a tune. On the other hand, Maya really felt humiliated.
