Stupidity: In the final reveal when Poirot gathers all the suspects for his reveal of the murders, he already knows that Jackie and Simon are the murderers. So why would he carelessly leave the loaded pistol on the table in clear view and an arm's reach of Jackie? That is very stupid for a trained and experienced detective.
Stupidity: In the original novel, the attempt on Mrs. Doyle at the temples was made rolling a boulder off a cliff. In this adaptation, the culprit is said to 'dislodge' a large stone from the temple; you can however see that the stone is already dislodged and sticks out from its place on the pillar, and he had no way to know that the Doyles would be in that particular spot, making this attempt to Linnet's life rather nonsensical (requiring also herculean strength, no pun intended). (00:47:40 - 01:39:30)
