In Roald Dahl’s “Lamb to the Slaughter,” Mary kills her husband using a leg of lamb, then serves it to the police officers that come to investigate the murder. The reader knows that the lamb is the murder weapon, but the police officers do not, which is an example of dramatic irony. Dahl’s choice of the lamb has both metaphorical and biblical implications.
Dahl’s choice of a leg of lamb is symbolic because it indicates Mary’s passivity being turned into a violent weapon. From the beginning of the story, the reader can see that Mary is submissive in her relationship with her husband. When he tells her about his affair, he expects her to accept his word and the consequences of his actions without a fight.
So there it is. … And I know it's a tough time to be telling you this, but there simply wasn't any other way. Of course, I'll give you money and see that you're taken care of. But there really shouldn't be any problem. I hope not, in any case. It wouldn't be very good for my job.
In this moment of emotional distress and turmoil for his wife, he does not put her at the forefront. Instead, he cares more about his own situation and how people at his job will perceive him. Mary’s passivity in their relationship can be connected to the symbolic connotations of a lamb—weak, defenseless, and trusting.
The symbolic connotations are heightened by the biblical symbolism of a lamb as well. Isaiah 53:7 says,
He was oppressed and afflicted, yet he did not open his mouth; he was led like a lamb to the slaughter, and as a sheep before its shearers is silent, so he did not open his mouth.
Throughout the Bible the followers are referred to as a “flock,” “sheep,” and “lambs.”
Through connecting Mary to a lamb, Dahl establishes her character and the type of marriage she is in. It also serves to strengthen the irony in the story, when something that is perceived as harmless is made violent.