The "poisonous toy becomes GHB" plot is based on an actual toy product recalled in 2011. Aqua Dots, or Bindeez, were made with a glue that if eaten turned into GHB, the "date rape" drug. However, there were no fatalities: 14 children became ill, and several fell into temporary comas.
In 1891 Sir Arthur Conan Doyle published a short story titled "The Five Orange Pips." In the story, a man is terrified when he receives five orange seeds in an anonymous envelope, knowing it is a threat from someone in his past. His death follows. Another man receives the pips and also dies. The remainder of the short story is not used.