Corrected entry: Poirot finds out from insurance documents that the surviving husband of the murdered Yorkshire woman in the beginning of the movie, Alice Ruber, was called "Felix Ruber." Poirot had been told by hotel guest Patrick Redfern, a Latin teacher, that "Giuseppe Verdi" means "Joe Green" when translated into English. Poirot explains during the murder's solution that this triggered him to translate the two Latin adjectives "felix" (strictly: 'filix', not 'felix') and "ruber" into "fern" and "red", respectively, and thus "red fern." It is part of the evidence that Felix Ruber and Patrick Redfern are one and the same person, meaning that Patrick was involved not only in the island murder but also in the Yorkshire murder.
Corrected entry: Poirot in his summing up of what took place in the murder of Arlena, makes many assumptions about exactly what took place on the beach, he said (in so many words) - Arlena went to the pedalo in order to leave the beach on it, but then ran in to cave instead. How could he possibly know this? There were no witnesses or evidence of this. All he knew was she must have gone into the cave as the gem stone was in there.