Factual error: Throughout this episode, the Japanese assassins are inaccurately referred to as "the Bushido." They should, as the episode title implies, be called Samurai. Bushido was the revered code by which Samurai warriors lived, but was never an appellation for them.
Factual error: Two deaths by bubonic plague, spread by casual human contact, have Five-O scrambling to prevent an epidemic on Oahu. But the disease isn't spread this way (its vector is fleas on infected rats). And since the introduction of antibiotics in the 1940s, bubonic plague has been imminently curable, so there was no need for panic, other than, of course, to make the episode more dramatic.