Shakespeare has already established Lady Macbeth's dominance over her husband in act 1. At this point in the play, Lady Macbeth displays her first moment of weakness to the audience, though she takes good care to hide it from Macbeth. She says that she has been in the king's chamber and could have killed him herself if he had not resembled her father as he slept. All of Lady Macbeth's castigation of Macbeth in this scene should be viewed with the recollection that he nerved himself actually to kill the king, when she could not.
Macbeth is nervous and distracted as he enters. Lady Macbeth tries to calm him and to persuade him to focus on the immediate practicalities of the situation, rather than the moral and philosophical implications of what he has done. She keeps telling him to stop thinking about what he has done, and she takes the daggers from him so that she can place them beside the sleeping grooms. At this point, their relationship is closer to that of mother and child than wife and husband. This is reflected in their attitudes to washing their hands. While Macbeth is convinced that "all great Neptune's ocean" will not suffice to wash away the guilt, Lady Macbeth is concerned only with the literal blood on their physical hands, admonishing him and saying, "A little water clears us of this deed." However, despite Lady Macbeth's fury, Macbeth is not cowed by her as he was in act 1. He seems to find the deed he has done so momentous and appalling that he forgets to be afraid of his wife.