At the beginning of the film, when The Soldier gets up and surveys the battleground, he stops to "play" with the arrow he sees piercing his body. He pushes the front down a few times and the part sticking out his back mirrors this movement. Of course, this would never happen, since it's a solid piece of wood, without any mechanism that would allow for this. It might be allowable as a joke on Jackie Chan's part, as is his wont.
Approximately 55 minutes into film you can see cacti on the tops of & growing alongside the ruined town walls. Cacti are not native to China and were only introduced in the 1800's AD. The story line would coincide with approximately 300BC. A difference of almost 2000 years.