“One of the things that you can see as a symptom of cyanide poisoning is someone having difficulty breathing,” said John Berry, a chemistry professor at the University of Wisconsin-Madison. “This happens very quickly.”
Berry said cyanide, which used to be in rat poisons because of its potency, can be combined with other substances to form gasses or salts that can dissolve in water. He also pointed out that cyanide is extremely difficult for someone outside of a research lab to get their hands on.