Factual error: The evil man request 100,000 pieces of gold for ransom. Each gold piece looks to be about 10 ounces, and 100,000 of those would make the entire thing weigh about 31 tons, but 2 guys are carrying it around in a little chest throughout the movie.
Factual error: Just before we see Roy O'Bannon's gang for the first time as they are preparing to rob a train, we see a shot of the train winding along track in a very picturesque valley. However, the tracks are paralleled by very modern telephone poles with several wires on them. If this was truly the old west, the poles would have had only a single wire on them for the telegraph service.
Factual error: During the train fight scenes, as they are hopping from wagon to wagon, you can see the wagons fitted with modern couplings to connect them together, rather than the throw-over hook and loop couplings that would have been fitting for the time the film was set.
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.