“the only way it would be known if Breitbart had been hit by a heart-attack-inducing assassination dart.”
Great thinking, and the exact same conclusion that I arrived upon when Breitbart was assassinated. In fact, it is seemingly the only possibility that he was assassinated by a poison dart ordered by Obama or George Soros.
The Bulgarian umbrella is the name of an umbrella with a hidden pneumatic mechanism which shot out a small poisonous pellet containing ricin. The Bulgarian Umbrella has a hollow stalk which the pellet neatly sits into. Such an umbrella was allegedly used in the assassination of the Bulgarian dissident writer Georgi Markov on September 7, 1978 (the birthday of the Bulgarian State Council Chairman Todor Zhivkov who had often been the target of Georgi Markov’s criticism), on Waterloo Bridge in London (Markov died four days later), and also allegedly used in the failed assassination attempt against the Bulgarian dissident journalist Vladimir Kostov the same year in the Paris Métro. The poison used in both cases was ricin.
Source: Wikipedia