After the opening, West and Gordon are on the train discussing opium. Although Gordon does not move from his seat on the couch, his shadow on the window changes location depending on the shot.
Artemus mentions that the people of Hunan speak Cantonese; the principal language of Hunan is Xiang (Hsiang); Cantonese is spoken in Guangdong (canton's home province), neighboring Guangxi province, Hong Kong and Macau.
The saying West refers to about an Oriental "...not being able to get into heaven without his pigtail" is spurious. The queue, as it was more properly known, was imposed by the Manchu Qing (Ch'ing) dynasty as a symbol of their overthrow of the Chinese Mings in 1644. Failure to adopt the queue was considered an act of sedition and was punishable by death; the official policy was "Keep your hair and lose your head, or keep your head and cut your hair". Hundreds of thousands of people were executed or even massacred, then denied a proper burial. When the Qing dynasty fell in 1912, the hairstyle disappeared almost overnight.
Artemus (in disguise) attempts to speak Mandarin (badly) to Wang Chung when they meet, Wang states that he only speaks Cantonese which is not spoken in Hunan. Wang then says, "Chop chop" while speaking English, a phrase which is of Cantonese origin. However, at the end of the scene when he speaks to his henchman in Chinese, he speaks in Mandarin.
Reference is made to the "Hunan Throne". Hunan has always been a province which, in the imperial days (the last imperial dynasty, the Qing, ended in 1912) was ruled by a governor appointed by the emperor. As such, there is no such thing as a Hunan Throne. The only throne in China referred to by name is the imperial one, called the Dragon Throne. Any reference to another throne would have been a hallmark of sedition and open rebellion to imperial rule.
Wang Chung refers to the passage of "Emperor Wu"; this is not the way a recently deceased emperor would have been named. Each emperor was given a "reign name", and was referred to as "The [Reign Name] Emperor". On death, each emperor was given a posthumous name. From 1861 to 1875, the ruler of China was the Tongzi Emperor, known after death as Yidi. He was succeeded by the Guangxu Emperor. During the reigns of both these emperors, the power behind the throne was Empres Dowager Cixi Taihou, wife of the Xianfeng Emperor (reigned 1850-1861). The last ruler known as "Emperor Wu" reigned during the Chen Dynasty, 557-559.
When Allenby-Smythe hands the execution sword to the Captain (Artemus in disguise), the latter holds it up in both hands with the edge pointing forward towards the camera. It can clearly be seen that the sword's edge is thick and rounded, and therefore merely a prop without a cutting edge.
Furthermore, the sword is a scimitar in the Arabian style. Chinese swords had straight blades, more closely resembling European swords.
In the opening segment, Artemus makes a reference to fortune cookies. Later West is seen breaking one open. The fortune cookie was an American invention of the early 20th century, and were based on a Japanese dessert called Senbei which became popular in the late 19th century.
The story centers on opium traffic. However, if one presumes that this action takes place early in West's and Gordon's careers as agents, it was probably before there were any legal restrictions at all on opium sale or use. In 1875 (probably after this story occurred), San Francisco passed an ordinance making opium parlors illegal but did not otherwise restrict its sale or use (and was motivated more by anti-Chinese than anti-drug sentiments). In 1897, the state of California passed a law requiring warning labels on narcotics and that purchases be registered. In 1907, opium was further restricted to prescription sales and was finally outlawed altogether (along with opium pipes) in 1909.
Col. Allenby-Smythe plans to sail to the "Gulf of Hunan". Hunan is a landlocked province; there is no such body of water.