In Roald Dahl's short story "Lamb to the Slaughter" Mary Maloney's mental state prior to the murder of her husband is relatively normal. I say relatively because she is immensely devoted to her husband, so dedicated that it would be possible to argue that she is obsessed with her husband. An example of her dedication to her husband is represented in the following quote,
“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.”
In this quote Patrick, Mary’s husband, is like the sun to her. He is a figurative and literal center of her world. The daily routines she has all revolve around her husband’s return home. The drink elements readied for his return, her knowledge of his every move and motion to the point of knowing he is drinking differently because the sound the ice makes against the glass, these are all examples of her near obsessive dedication to her husband.
After she kills her husband it is not hard to say that she has a psychological split from reality. At first she knows what she has done, killing her husband. Mary tells herself, “So I've killed him.” After the realization of her actions she is calm and thinks about the repercussions of her actions. She only starts to become concerned when she thinks of her unborn child. Here is where Mary starts to split from reality. She plans her actions, cooking the murder weapon and practicing acting normal to establish an alibi with Sam the grocer. All these actions could still be considered sane but illegal. It is her return trip home where the break occurs.
“And now, she told herself as she hurried back, all she was doing now, she was returning home to her husband and he was waiting for his supper; and she must cook it good, and make it as tasty as possible because the poor man was tired; and if, when she entered the house, she happened to find anything unusual, or tragic, or terrible, then naturally it would be a shock and she'd become frantic with grief and horror. Mind you, she wasn't expecting to find anything.”
She creates a scenario that she starts to believe so that when she does see her husband the reaction to his death is genuine. Although she seems to have broken away from reality, she does have moment of understanding as seen when she is aware of the irony, giggling when the officer eating the murder weapon says that the murder weapon is “probably right under our very noses.”
Mary goes through several mental states as the story progresses. She is dedicated and devoted loving wife, rational yet homicidal, cold and calculating, separated from reality, and acutely aware.