- Hiding In Plain Sight: In one adaptation you can actually see the killer poison Marston's drink.
- Market-Based Title: Possibly the only example in the Agatha Christie canon where the American title is the one used by publishers in both the US and the UK and Commonwealth (for obvious reasons).
- Name's the Same: Mr. Rogers and General MacArthur.
- Referenced by...: The name of the Touhou song "U.N. Owen Was Her", used as a bonus stage theme in multiple games, is a nod to the name given to the killer.
- Science Marches On: Improvements in forensic science since 1939 would have allowed the police to figure out that Wargrave's actual time of death was significantly later than what it was reported to be in the diaries of the guests who lived long enough to find the 'body'.
- Not Necessarily. His time of death was reported to be around 6:20, but the guests might not have written when he died, so much as the fact that he did.
- What Could Have Been: Vera's original motivation was poisoning her husband's lover. That was deemed much too bland and Cyril was born. The movies use it anyway.
Trivia / And Then There Were None