The dead woman who is found at the beginning of the movie takes a rather deep breath at the end of the shot.
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.