Perhaps the most prominent theme in Roald Dahl's story "Lamb to the Slaughter" has to do with the sudden and surprising change that comes over Mary Maloney when her husband tells her he wants a divorce. She was herself literally a "lamb" up to that point, but she changes into a murderess and kills her husband with one blow in a violent outburst of rage. The theme has been a common saying for centuries.
Hell hath no fury like a woman scorned.
It was originally derived from William Congreve's play The Mourning Bride (1697), in which the character Zara says:
Heaven has no rage like love to hatred turned,
Nor hell a fury like a woman scorned. Act 3, Scene 7
A good example of love to hatred turned can also be found in Medea (431 B.C.) by the ancient Greek playwright Euripides (480-406 B.C.). But many examples can be observed in our everyday modern life, or read about in the newspapers.
The most striking thing about "Lamb to the Slaughter" is not that Mary Maloney gets away with her crime, nor that she has the investigating policemen eat up the murder weapon, but it is the totally surprising change in her meek, loving character which motivates her to kill her husband with a single, violent blow to the head with a frozen leg of lamb.