of her husband in "Lamb to the Slaughter." Her love turns suddenly to hatred, an alteration that happens so quickly that she herself seems to be unaware of it until she has actually killed him. Her rage is violent and automatic, as the frozen leg of lamb falls on Patrick's head like a thunderbolt from heaven.

This sudden violence from a woman who seemed unusually placid and serene until this point is caused by Mary's reaction to Patrick's infidelity and desertion. She is "a woman scorned" because Patrick has decided to abandon her, even while she is pregnant. There is something extreme about Mary's devotion to her husband even at the very beginning of the story:

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.

This seems more like the infatuation of a teenager than the stable love of a married woman. It is because her love for Patrick is so extreme as to be unbalanced that her reaction to his infidelity is equally extreme. She adored him with such intensity that she could not bear his abandonment.

This question can be answered through a close reading of the text; Dahl doesn't directly state the reason, but it can be inferred from clues given.  If you look carefully at the story, it indicates that Mary was waiting contentedly for her husband to come home from work.  He does, and she waits  on him hand and foot, wanting to please him and make him happy.  However, he seems a bit distracted this evening, and drinks his entire cup of whiskey all at once, and is nervous.  Finally, he tells her that he is leaving her.  Roald Dahl writes,

"And he told her...he added... 'Of course I’ll give you money and see you’re looked after.  But there needn’t really be any fuss.  I hope not anyway.  It wouldn’t be very good for my job.'"

These lines hint at the fact that he has just relayed the horrific news that he didn't love her anymore and didn't want to be with her. Dahl doesn't relate the exact words that he says, but we can infer it from the fact that he says he will give her money, that he doesn't want any fuss, that it is bad news, etc.  And, Mary's shock at the news also implies that her husband, who she was very happy with, appears to be abandoning her and their unborn child.

This is reason enough for her to lose it.  In a daze, she goes down to get meat for dinner, and before she even realizes what she has done, she bashes her husband over the head with the frozen leg of lamb.  The reason is her shock and dismay at a man who she loved so dearly betraying her and leaving her and her baby to fend for themselves in the world.

I hope that those thoughts clear things up a bit; good luck!

A careful examination of the text shows readers that Patrick or Mary never says the word "divorce." We can't be 100% sure that Patrick wants a divorce:

"This is going to be a bit of a shock to you, I’m afraid," he said. "But I’ve thought about it a good deal and I’ve decided the only thing to do is tell you right away. I hope you won’t blame me too much."

And he told her. It didn’t take long, four or five minutes at most, and she sat very still through it all, watching him with a kind of dazed horror as he went further and further away from her with each word.

"So there it is," he added. "And I know it’s kind of a bad time to be telling you, but there simply wasn’t any other way. Of course I’ll give you money and see you’re looked after. But there needn’t really be any fuss. I hope not anyway. It wouldn’t be very good for my job."

It is conceivably possible that he wants to separate from Mary and live separate lives but not tell anybody and not have a legal document attached to his name that says he is divorced. This arrangement could be why he says the line about "it" not being good for his job. Perhaps a divorce would reflect badly on him and his work situation.

Regardless of what Patrick wants, it is clear that the marriage is over. Unfortunately, readers never learn what Patrick's motive is. That's okay because it's not the point of the story. Mary's transformation from hearing his terrible announcement is way more important to the story. Additionally, Dahl has created an interesting discussion topic by not telling readers why Patrick does what he does. Perhaps he has found another woman. Perhaps the thought of being a father is too much for him to handle. Perhaps Mary is too much the doting wife, and he feels stifled at home.

In "Lamb to the Slaughter," Dahl does not reveal to the reader Patrick's reason for wanting to divorce his wife, Mary. Instead, the reader experiences this moment from Mary's perspective. As we might expect, such a shocking announcement happens in a blur for Mary: she is unable to grasp the details because his announcement is so unexpected. This is shown through Dahl's description of Mary's reaction:

She sat still through it all, watching him with puzzled horror.

In contrast, Patrick is relatively calm and collected: he responds to her in a very matter-of-fact way by emphasising the practical matters of the divorce, like the financial settlement. Ironically, he thinks that the worst is over because he has broken the news to Mary, not realising that his murder, the worst possible outcome, is about to take place.

Mary Maloney, the pregnant wife of a police officer, is the main character of Roald Dahl's short story "Lamb to the Slaughter". In the story her character is described, mainly through her actions, as a doting and devoted wife and homemaker.  The way in which she keeps her home, the manner in which she prepares for the daily return of her husband from work, and the excitement that she exhibits as she waits for his return leaves the reader with no doubt that Mary is a woman who is happy and in love. So much in love, in fact, that Roald Dahl is emphatic about the manner in which she feels about her husband.

She loved to luxuriate in the presence of this man...  She loved him for the way he sat loosely in a chair, for the way he came in a door, or moved slowly across the room with long strides. She loved [the] far look in his eyes when they rested in her, the funny shape of the mouth, and especially the way he remained silent about his tiredness..

However, her actions come to a shocking halt when, after her husband tells her that he wants to leave her, she is in such a shock that she enters her kitchen, grabs the first big object that she finds, and then goes to her husband and crushes his skull with it.

What this denotes is that Mary has snapped. While she has no real reason to motivate her to kill her husband, it is obvious that the creeping fear, anger, hurt, and frustration of the news have come altogether dangerously. That, added to the fact that she is pregnant and already in a delicate state, may be the reasons why her reaction was so extreme. However, it is hard to blame a woman who is so happy and protected not to at least wish hurt upon whoever comes across her territory. Although her actions are not justifiable, it is almost understandable that Mary's world has come crumbling down by the choices of what seems to be a cold and callou husband.  Therefore her main motivation may not be to get rid of him altogether but certainly she would have wanted to exert all of her anger upon the person who caused it; her husband.

Choice D.  Mary is heartbroken that Patrick would leave her.  Of the four choices that are listed there, that is the best choice.  

The opening paragraphs of the story clearly show readers that Mary is deeply in love with Patrick.  When the story begins, readers are told that Mary is patiently waiting in the front room for her husband to get home.  She is not only waiting though, she is excitedly waiting.  

Now and again she would glance up at the clock, but without anxiety, merely to please herself with the thought that each minute gone by made it nearer the time when he would come.

The above lines say that Mary kept checking the clock in order to know that each minute passing was another minute closer to seeing Patrick.  That's something my kids do when grandma and grandpa are coming over.  They constantly ask me what time it is or "how much loooonger."  They can hardly wait because they are so excited, and they keep clock checking to make sure that time is indeed passing.  

Once Patrick arrives at home, Mary flutters about the house making sure that Patrick merely has to sit down and enjoy his rest.  She gets up to greet him, she gets him a drink, and she is happy to merely sit quietly next to him.  

For her, this was always a blissful time of day. She knew he didn’t want to speak much until the first drink was finished, and she, on her side, was content to sit quietly, enjoying his company after the long hours alone in the house. 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. She loved him for the way he sat loosely in a chair, for the way he came in a door, or moved slowly across the room with long strides. She loved intent, far look in his eyes when they rested in her, the funny shape of the mouth, and especially the way he remained silent about his tiredness, sitting still with himself until the whiskey had taken some of it away.

He is her entire world.  When he calmly tells Mary that he is leaving her, Mary is devastated.  She's completely blindsided by it, and she is left stunned.  

It didn’t take long, four or five minutes at most, and she say very still through it all, watching him with a kind of dazed horror as he went further and further away from her with each word.

As Mary moves about the house in a daze, Patrick tells her that he will be going out again.  It's the final straw.  Mary can't believe that Patrick would stop loving her.  She can't fathom it, because she doesn't feel anything like that at all.  She feels hurt and devastated, and hitting Patrick over the head with the leg of lamb is likely her way of making Patrick feel some pain too.  Unfortunately (fortunately?) the blow to the head kills Patrick.