Polly once wondered how and why slaves put up with so much abuse, and if slaves could even feel pain. This incident makes several things abundantly clear to her: slaves are people and absolutely feel pain, and they submit to the abuse because they literally have no other choice. Polly’s insistence that Mr. Derby probably tripped Amari speaks to how disillusioned she is with the plantation—and possibly, she’s disillusioned with becoming an upper-class slave owner more broadly. It’s a mark of how much Polly has changed that she focuses on healing Amari instead of wallowing about not being able to work at the house.