There are a couple of ironic points to this story. First of all, the title is a pun. A lamb to the slaughter usually refers to someone who is unaware they are about to be harmed, since lambs are easily led to their slaughter since they trust the one leading them and they are unaware of what is to become of them.
In this story, the husband, Patrick Maloney, is killed like a lamb, totally trusts his wife Mary and is completely unaware of his impending doom, but the title is also ironic because it is actually a frozen leg of lamb that is used to slaughter the hapless victim.
The final irony is dramatic irony, because the reader knows that the leg of lamb was used as a murder weapon, but the police unwittingly eat the evidence when the killer serves the roast leg of lamb to them.
One example of verbal irony in the story occurs just before Mary learns that Patrick is leaving her. When discussing dinner options, she says, "There’s plenty of meat and stuff in the freezer, and you can have it right here and not even move out of the chair." Looking back, this is ironic because Mary does in fact bring the leg of lamb into the living room. Patrick "has" the lamb, but certainly not in the same way that Mary intended when she said this to him earlier in the story.
Another example of verbal irony occurs later in the story after Patrick is already dead. Mary has put on a little show for the grocer and she goes back into the house and calls to her husband, "How are you, darling?" She obviously knows that he is dead, so her asking how he is doing is quite ironic.
Dramatic irony occurs when the audience has knowledge of something that some or all of the characters do not, and because of that words or actions have a different meaning. In "Lamb to the Slaughter" the reader knows that Mary Maloney, having been told by her policeman husband that he is leaving her, has killed him with a frozen leg of lamb. The dramatic irony occurs when she cooks the lamb and serves it to the men investigating her husband's death while they speculate about what the murder weapon might have been and where is could be. In fact, one of them remarks the evidence they are seeking is probably "right under their noses." The reader knows they are eating the very weapon they are seeking! That is dramatic irony.
Situational irony occurs when something that happens is the opposite of what we would normally expect to happen or find appropriate. Certainly, the major piece of situational irony is found when Mary Maloney, who Dahl goes to great lengths to depict as a loving wife who is devoted to her husband, in a moment of madness, kills him. Consider how she is introduced:
For her, this was always a blissful time of day... She loved to luxuriate in the presence of this man, and to feel - almost as a sunbather feels the sun - that warm male glow that came out of him to her when they were alone together.
Mary Maloney is presented as being so obsessed with her husband that nothing is too much to ensure his comfort and happiness. Then it is a complete shock to us as readers when she kills him with the frozen leg of lamb:
At that point, Mary Maloney simply walked up behind him and without any pause she swung the big frozen leg of lamb high in the air and brought it down as hard as she could on the back of his head.
This action is completely the opposite of what we would expect a character like Mary to be able to do. The second piece of situational irony comes when she manages to very coolly and in a calculating fashion organise an alibi and the removal of the murder weapon. Consider the last line, where Mary celebrates the success of her plan:
And in the other room, Mary Maloney began to giggle.
Again, this criminal behaviour and outwitting of the policemen is not the kind of activity we would expect to see from a devoted housewife. Both of these incidents serve to shock us in the story through the use of situational irony.
Another example is the very last line of dialogue in the story. The officers are consuming the leg of lamp and discussing the murder while, obviously, digesting the murder weapon. Then one officer states that the weapon is "probably right under our very noses." And, of course, it is.
- Verbal irony, dramatic irony, and situational irony are used in this story.
One of the most important examples of irony in 'lamb to the slaughter' is when the detectives are eating the leg of lamb and say, "its probably right under our noses". This is an example of dramatic irony because you know the weapon they're looking for is literaly under their noses.
The irony is in life and in this story is there are many innocent who are led by individuals to harm unknowingly, some continue to be led by the same person, and then by others. It seems lambs or trusting, gullable people make easy targets, over and over again
Patrick Maloney is the very trusting individual that is killed like a lamb, he absolutely trusts his wife Mary and never would think of her as causing him harm. The other ironic thing that happens is the frozen leg of lamb is the murder weapon used to kill Patrick. Then the leg of lamb, the very evidence and murder weapon is eaten by the police.
When Mary went to the grocery store and came back and asked her husband if he was o.k knowing that he was already dead.
The dramatic irony in the story is when the cops cannot find any weapon and one of the cops says, "Weapon might be right under our nose", because it really is, it's the lamb they are eating.