Jane Helier comes across as even more vacuous than usual when she is telling her story, "The Affair at the Bungalow". This makes perfect sense with the revelation that the scenario she was describing hadn't even happened yet, so she did not have any memories to go on.
An example that crosses over with Fridge Horror: in "The Four Suspects," Dr. Rosen is perfectly aware that his work destroying the Schwartze Hand terrorist group will result in his own murder. It seems like a logical conclusion, until you remember that he disbanded the Hand by becoming a member, gradually rising through its ranks, and eventually exposing them. This means that Dr. Rosen likely knew that his niece Greta, who lives with him, was also in the Schwartze Hand—naturally the high-ranking members of the group would know its agents. When he goes to see Sir Henry Clithering to tell him that the Schwartze Hand will be sending a member to murder him in revenge, he already knows that Greta will be the one to do it. He probably refused to expose her out of familial love and may have even hoped that her own affections for him would be returned in kind, although given his intelligence, he was likely prepared for the worst.
Another one from "The Four Suspects": since the solution to the mystery hinges on the mail delivered to Dr. Rosen on the day of his death, it seems odd that Sir Henry would have that mail with him during a dinner party with the Bantrys. But then you remember that Sir Henry was the one who invited Miss Marple to that party in the first place—he was likely going to consult her about it during his visit to St. Mary Mead anyway (given how much he respects Miss Marple's intelligence as proven in the original meetings of the Tuesday Night Club), and simply used the gathering to kill two birds with one stone!
In "The Bloodstained Pavement", Joyce tells how she encountered The Bluebeard, who always had the same scheme: he met lonely young women without many people to notice what happened to them, insured their lives, and 'happened' to run into an old friend - his real wife - who would join them bathing, kill the young woman, and the wife would take her place until they could fake the victim's death in another place a day or so later. Joyce explains that he was caught because he used the exact same plan every time - and the insurance companies became suspicious. Given that he must have used a different insurance company every time, how many women did he kill before enough different companies got together to compare notes? Given that it's implied the killer was on his honeymoon with each wife when she died, he and his real wife could have killed over a dozen young women before getting caught.
