Revealing mistake: This mistake occurs in the beginning of the film where the bandits rob the train. When Jackie is standing on the coal (or was it wood?) car you can see the train is passing a modern sign (you can see it on the right).
Revealing mistake: At the end, when Jackie is fighting the bad guy, he jumps up into a windowsill and then jumps down when the bad guy tries to hit him with a spear. If you look at the spear when it hits the wall, you can see that the spearhead is made of rubber because it bends when it touches the wall.
Revealing mistake: When Roy and Chon are escaping from jail, Chon uses all his strength to bend one of the iron bars aside so that Roy can squeeze through. But, as Roy squeezes through, the iron bar behind him (which should be rigid) also visibly flexes, revealing that the bars are made of rubber or plastic tubing.
Answer: During the Qing Dynasty it was compulsory for men to wear a queue to prove loyalty to the Manchu rule. Refusal to follow can result to execution considering that as treason. Also, he not only prevented him from going back to China but also preventing him from informing the Emperor of his crimes without his queue.
Yes, but in fact, Jackie Chan wasn't wearing a queue in the movie. He only had the pony tail. His head should have been shaved half bald, especially if he was the Emperor's Guard. They just didn't want to show Jackie Chan in a half-bald hairstyle.
Similarly happened in 1976 film Hand of Death in which Jackie co-starred in. That film too was set in the Qing Dynasty but all men still had their queues but no shaved temples. The slaves in Shanghai Noon however some of them did actually have that hairstyle correctly having both queue and front temples shaved bald.