1. Similarities: Both stories feature seemingly innocent females outsmarting males (interestingly enough, both stories are written by males!). Vera from "The Open Window" seems like a romantic, innocent girl who politely greets her aunt's visitor. Mary Maloney in "Lamb" is a pregnant, dutiful wife to whom the police cater as they investigate her husband's death. Vera preys on the overly anxious Framton Nuttle, while Mary deems herself betrayed by her husband and murders him. In the end, both women effectively cover up what they have done to "victims."
2. Differences: Vera's "torture" of Framton is motivated by a prankish spirit. She does not want to kill Framton; she simply desires to try out her storytelling techniques on an innocent victim. Mary Maloney, on the other hand, is motivated by a spirit of revenge after her husband informs her that he is leaving her. She intentionally murders her husband.