One of the spookiest elements in the short story "Lamb to the Slaughter" by master story-teller Roald Dahl is Mary's coolness. We see her cool, calm, and collected at the beginning of the story totally in control of her environment and the situation. She has everything done to a tee - dinner, drinks, calmness. Some men would appreciate that - others may feel smothered by it. Is that why Patrick leaves? But she is not in as much control as she thinks she is - she is so smug she has read her own supposedly-loved husband's body language wrong and he is obviously living a second life. How could she be so blind? Perhaps she is just a bit too smug. The spooky thing is that at the end she loses her self-control (tellingly as icy as the freezer itself!) by letting out a giggle. She is almost dissociated from what she has done - perhaps in the numbness of shock or a pathological psychological personality.
At the beginning of the story, Roald Dahl depicts Mary Maloney as being the portrait of the docile, devoted wife. As she sits with her sewing,
. . . 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.
Everything is prepared for his arrival: "On the sideboard behind her, two tall glasses, soda water, whiskey. Fresh ice cubes in the Thermos bucket." Her love for her husband is described in such exaggerated terms by Dahl that it borders on obsessive:
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.
That's almost too much to handle, don't you think? But Dahl is setting us up: By elaborating so much on how attached Mary is to her husband, he is preparing us to--at least somewhat--understand her actions. When Patrick breaks the news to Mary, presumably that he is leaving her, despite the fact that she is pregnant, she snaps. There's no other way to explain it--she pretends he hasn't spoken, and proceeds to fix dinner. Once she whacks him on the head and kills him, she puts on a happy face and plots her alibi. But perhaps the strangest part of Dahl's depiction of Mary comes at the end of the story, when the other officers are eating the murder weapon, and Dahl tells us that "in the other room, Mary Maloney giggled." Creepy. So it is ironic that Dahl takes us from our original understanding of Mary as this gentle, loving housewife to a cold, calculated murderer of the very man she loves so much.