As was mentioned in the previous post, Lady Macbeth has made herself bold by drinking the same alcohol that she gave Duncan's chamberlains. After she claims that the alcohol has made her bold, Macbeth exits Duncan's chamber. Macbeth is visibly perturbed and tells his wife that he heard the servants say,
"Glamis hath murdered sleep, and therefore Cawdor shall sleep no more. Macbeth shall sleep no more" (Shakespeare, 2.2.42-43).
Lady Macbeth reveals her bold nature by commanding her husband to stop being a coward. Despite the fact that Lady Macbeth is unable to murder King Duncan herself because he reminds her of her father, she takes matters into her own hands by returning the bloody daggers to Duncan's chamber. Lady Macbeth again reveals her bold character by telling her husband,
"Infirm of purpose! Give me the daggers. The sleeping and the dead are but as pictures. 'Tis the eye of childhood that fears a painted devil" (Shakespeare, 2.2.52-55).
In relation to Macbeth's earlier quote about God's justice bringing the poisoned chalice to their own lips, Lady Macbeth's bold actions eventually come back to haunt the couple. Together, Macbeth and his wife have successfully assassinated King Duncan. Throughout the remainder of the play, both characters are forced to deal with the negative consequences of their actions. Lady Macbeth becomes so consumed with guilt that she eventually loses her mind.
Lady Macbeth has drunk some of the drugged wine she prepared for the grooms: "That which hath made them drunk hath made me bold." The success of the drink is mixed at best. She says she would have killed Duncan herself had he not looked like her father while he slept; on the other hand, when Macbeth is unwilling to return the bloody daggers to the murder scene, she not only does so but also smears the grooms with blood. She has no fear of the dead king.
Macbeth's statement, made before he offers several reasons for not killing his king, logically points out that as much as he wishes that this act of murder would be the one act necessary to accomplish his goal, he realizes that by killing the king, he and Lady Macbeth simply teach others how to murder. They may then be victims themselves later. The "poisoned chalice" refers literally to the potion that Lady Macbeth provides for the grooms. Macbeth realizes that their plan may backfire; they may be caught in their net.