After the prostitute tells Cheng about the drug smuggling, he leaves. She is sitting with her back to the door when Mi's son sneaks in. You hear the knife flying through the air and see her face as it hits her in the chest. If she had her back to the door, how did the knife embed in her her chest?
The knife in the villain's chest disappears after Cheng punches him multiple times on the ground.
Despite receiving a deep cut to his left arm the night before, Cheng has no scar on his left arm the next day while fighting "The Boss".
In the last fight, the dead henchman in red turns his head from one side to the other from shot to shot. This is most prominent when "The Boss" throws his knife in the end (and the subsequent "kickback").
As Chao-an leaps over the fence in the finale, the bag of crackers he's holding disappears and then reappears after he lands.
When the guard dogs leap at Cheng, they are obviously thrown.
During the fight inside the ice factory when Cheng gets caught, he ducks down a little too obviously before his opponent throws an object at him.
When Hsiu Chien and his brother are fighting at the Boss' house Chien's brother gets an ax thrown in his back the shape of the blood bag is clearly visible.
When Cheng Chaon slides the ice down the ramp and it crashes, a bar can be seen placed on the ramp to assist the crashing.
In the final fight, The Boss throws a knife at Cheng. It is clearly seen to fly over Cheng's head as he ducks. Cheng falls to the ground and kicks the knife back, near ground level.
After the hooker tells Cheng about the drugs at the ice factory, Cheng immediately goes to the ice factory to investigate and the hooker is killed by Mi's son. When Cheng gets to the ice factory, he finds the hooker's body frozen in a block of ice. This would be impossible, since it would take many hours to freeze a person's body in a block of ice that size.
When Chao-an and "The Boss" face off, when "The Boss" pulls out his knives for attack, he slashes Chao-an once across the stomach, and once across the back. However, when slashing at his back, a sound effect implies that he misses, when a scar can be seen on his back seconds later.
When the gambling crooks catch up with Hsiu Chien and Cheng Chao, Hsiu Chen says to them "So just you 4 lousy guys?" However, there are clearly 6 men standing in front of him.