Continuity mistake: Poirot is holding up a letter in an envelope. He turns it to show the front to Lady Mayfield. The flap of the envelope appears to be tucked in. The shot cuts to a close-up, but now the back of the envelope is facing Lady Mayfield and the flap is sealed. He then turns the envelope to show her the front. (00:44:20)
Other mistake: Mrs Vanderlyn holds a letter out of the car window and calls to the chauffeur to take it. She calls him "Dixon" but the subtitles read "Gibson". (00:37:05)
Factual error: The basis of the blackmail is based on the Japanese invasion of Manchuria because howitzers were supplied to bombard Shanghai. Shanghai is not in Manchuria. (00:35:41)
Plot hole: Hastings came over to assist Poirot in his case, posting guard overnight. He offers to drive Poirot back to the villa since Poirot is in a rush and has figured out of the culprit. Poirot approaches the villa just in time to come across Mrs. Vanderlyn on her way out. Poirot rushes to Hastings then to give chase to the woman but...Hastings has pulled out all the plugs and is cleaning the carburettor, just doing some random maintenance to the car that would take him, in his words "an hour" to bring back to work. On a one-day job, Hastings crippled their own car for no reason whatsoever. This is beyond stupidity.
Continuity mistake: When Miss Lemon announces the anonymous caller to Poirot through the window, she holds the receiver at noticeably different heights between the consecutive shots. (00:09:00)
