This is representative of the poison that Mrs. Lorrimer used to kill her husband. She never gives the reason for the killing, and this impresses Poirot, who states that most women would attempt to justify their killings, if they were ever discovered.
These are representative of the expensive stockings that Poirot bought to test if Anne Meredith was a thief. As two of the pairs were missing at the end of Meredith's visit to his home, Poirot was able to successfully conclude that Anne was indeed a thief.
This is representative of the attorney that Major Despard uses as the reason to visit Anne Meredith and her friend, Rhoda Dawes. During one of his visits he manages to save the life of Rhoda, whom he falls in love with.
This is representative of Colonel Race, a British Secret Service agent invited by Shaitana to the party in which Shaitana was killed. Race discovers later the killings that Doctor Roberts, Shaitana's killer, had committed before killing Shaitana himself.