Natasha responds immediately, but while her movements are faster and stronger than human, they're not what they should be. Her face is expressionless, a mask that hides her frustration when she's not as strong as her attacker. She has to make up for it by being smart, perceptive, and well trained—and she does just that.

She regrets that she gave up on human blood now. Or she regrets the consequences of it, at least.