The paper boy at the newsstand announces "Gershwin dies!" Poirot opens the newspaper, which features the obituary of famed American composer George Gershwin. On the opposite page is the obituary of Laura Welman, and the date on the newspaper states that it is September 1937. George Gershwin died on July 11, 1937.
The red climbing roses featured in the episode are said to be the Zephirine rose, but the Zephirine rose is pink.
In the kitchen with Nurse Hopkins near the very end of the episode, Poirot shows her what is supposed to be a real rose. In the bright light of the kitchen one can clearly see the plastic stem running along the underside of the leaves, so the rose used is actually a fake satin rose.
When Poirot gets into a taxi he asks to be taken to 'The British Library.' This was not created until 1973. He should have asked for 'The British Museum' or 'The British Museum Library.'
Right before the scene where Elinor Carlisle observes Roddy and Mary kissing, there is a panning shot of the stairs and the hallway - at the end of the shot, a man in a red t-shirt, jeans, and sneakers steps into view in the background.