Revealing mistake: Right after Jake escapes from Tao's pinning him to the track towards the end, Tao is electrocuted, then falls to the tracks. When he stands up, he sees a train heading towards him. He cries out, sticks up his arms, and is hit by the train. In a quick shot just as the train hits, him, however, it is painfully obvious that it is actually a dummy that was placed in front of the train.
Revealing mistake: During the shootout with the police outside of the bar, Jake is inside, trying to fight his way out. When you first see him, he is taking on Serrano's right hand man and another guy. At one point, he jumps up, and a quick cut shows that he used both legs to kick the guy in the chest, sending him flying over the bannister. Look carefully, though - you can see that Jake actually just hopped up and then put his legs back onto the floor just before the shot cut to him kicking him in the chest.
Revealing mistake: Towards the end, when Jake is fighting Tao on the subway, there is a quick shot of Tao using a metal rod to keep Jake pinned to the train track as the train is coming. The train appears to be coming at normal speed, but watch the movements of Tao and Jake. It looks like you're watching a video tape that you forwarded while still watching it. It's obvious that they filmed the scene in slow motion and then sped up the film, yet Tao and Jake were moving at normal speed when they filmed it.