"Well, if we keep on circling, I might get bored. How comfortable are you with it being known that you let a woman lose interest?" Natasha isn't going to be baited into rushing him first. She's aware that he knows how she fights, but she's not sure if he is feigning ignorance or if he's truly forgotten her, if he's truly unaware that she also knows how he fights. His first attack will tell her. Then she'll know how she wants to play this. So she can wait it out, like she's got all the time in the world.