Revealing mistake: Towards the end of the preliminary murder scene inspection, look at the victim in the last close-up, following the part when Poirot picks up paper from the basket. Specifically, the gun hand: the pinky finger of the supposedly dead person, after being too long in the unnatural position, trembles a little. (00:07:30)
Revealing mistake: Poirot is sitting reading the paper with the front page visible to the viewer. A breeze ruffles the pages and reveals that the interior pages are blank. (00:14:10)
Answer: He definitely says "Belgian", but the subtitles get it wrong and show him saying "American."
Wblank71