What does the quote “We have scorched the snake, not killed it: ...Remains in danger of her former tooth,” mean in Macbeth?
We have scotch'd the snake, not kill'd it.(15)
She'll close and be herself, whilst our poor malice
Remains in danger of her former tooth. (Act 2, Scene II)
Macbeth tells Lady Macbeth that he is worried that there is still a threat to his kingship, so he needs to take further action.
This conversation takes place after Macbeth has killed Duncan. He was convinced to do so by Lady Macbeth. Once king, Macbeth is not satisfied. He decides that Banquo is a threat, because he knows about the witches’ prophesies that his sons will be king after Macbeth.
Our fears in Banquo
Stick deep, and in his royalty of nature
Reigns that which would be fear'd. (Act 3, Scene 2, p. 42)
Macbeth is worried that Banquo will betray him, or even that he might be suspicious that Macbeth killed Duncan.
Lady Macbeth tells her husband “What's done is done” (p. 45). She is convinced that all they needed to do was kill Duncan and then everything would be fine.
Macbeth is worried though. When he tells her they have “scotch’d” the snake and not killed it, he is using the snake as a metaphor for the threat to his being king. They might have killed Duncan, but they are still not safe. The “former tooth” can come back to get them. There are people who are a threat to them, and they have to be dealt with.
Better be with the dead
Whom we, to gain our peace, have sent to peace,
Than on the torture of the mind to lie
In restless ecstasy. (Act 3, Scene 2, p. 45)
Macbeth is worried. Lady Macbeth still does not know how much. She finds out during the dinner, when Macbeth acts strangely seeing Banquo’s ghost. She begins to doubt their actions, leading to her eventual downfall into madness.
Macbeth’s reaction to becoming king is indicative of his personality. He has what he wanted, but he is afraid to lose it. Lady Macbeth assumes that they are fine. They have what they want. She has underestimated her husband’s arrogance, greed, and paranoia. He is about to go on a killing spree to eliminate these so-called threats, and in the end it destroys both of them. She succumbs to guilt and loses her mind, eventually killing herself. Macbeth’s murder of Macduff’s family causes the man to get his revenge at all costs, and Macbeth loses his head—literally.