Her portrayal of Mammy is quite good -- like the bits where she's trying to talk some sense into Scarlett's character, reminding Scarlett that Ashley is Melanie's husband & so forth... 
That's what the Academy thought, too!
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I watched the Keira Knightley
Pride and Prejudice.
Worst. Adaptation. Ever. Boring, anachronistic garbage, and Keira Knightley made Liza Bennet seem like a spoiled, snotty, miserable jerk. And Mr. Darcy was a weak little babyman.