Continuity: When Elvira Blake and Brigit Milford enter the dining room and talk to Miss Marple, Brigit is in front. When the scene cuts back to them a second later, Elvira's shoulder is in front of Brigit's. The cut is too quick for their positions to change.
Anachronisms: In the scenes on the hotel roof, a modern siren/ alarm /loudspeaker can be seen attached to the building (approx 1980s or later technology).