The Adventure of the Cheap Flat - S2-E7
Factual error: When Poirot asks O'Brian about unsolved crimes with young couples as suspects, he says "There's that Bonnie and Clyde of course, but they're at large somewhere in the American Midwest", to which Poirot replies "And let us hope that is where they remain." Bonnie and Clyde were killed in Louisiana on May 23, 1934. The episode is set in October 1935. (00:12:20)
The Adventure of the Cheap Flat - S2-E7
Factual error: Agent Burt brushes off Poirot's question saying "When will you guys understand there is no such thing as the Mafia, the Black Hand or the Cosa Nostra?" The last term he uses, while not impossible (since members of the organization were indeed referring to it as such) is a huge improbability, considering that officially FBI (and certainly the general public Burt is lashing at) came to know the real name (adapted in "La cosa nostra") only decades later with the Valachi investigations. (00:24:05)
Answer: He definitely says "Belgian", but the subtitles get it wrong and show him saying "American."
Wblank71