When reporting the second murder to the police on the phone, Miss Marple uses the phrase "Murder most foul". A quote from William Shakespeare's "Hamlet", it was reused as the title of the following Miss Marple movie.
At the scene of the second murder, while Miss Milcrest is being interviewed by Miss Marple and Inspector Craddock you can see a number of figurines behind Miss Craddock. Some in a cabinet and some on a shelf along the wall to the left of said cabinet. Some of the figurines on the shelf dipict the Wizard of OZ. It starts with the Tin Man Dorothy possibly the Scare Crow and then the Witch. (Working right to left along the shelf to the corner and continuing along the wall). It's possible the Lion is placed behind Miss Millcrest'a head.