The scene where Sherlock "poisons" John's coffee always reminded me of a documentary I had seen once. It showed a scientific test design used in psychology studies. Now I have finally found the original article:
http://www.sciencedirect.com/science/article/pii/S1053811908000876
The scientists wanted to test the brain activity of persons who were confronted with questions involving moral judgement. They made up the story of "Grace". Grace took her friend on a tour of a chemical plant and then Grace poured them coffee. Different scenarios are presented, all about the question a) if the sugar is poisonous or not and b) if Grace thinks that the sugar is poisonous. The test was meant to show how people judge Grace if she deliberately or unknowingly puts poison into her friend's coffee.

The original article is about brain activity, but from what I understood the test is also commonly used for studies with high functioning autistics, to see in which way their reactions and moral judgements are different from those of other people.
I wonder if this reference in the episode was intended or not.