Revealing mistake: Before Paxton is hit with the 3 prong instrument, you can see the bloody holes already on his shirt. (01:01:20)
Revealing mistake: Very obvious that Kana has a rubber prop and eye attached to her face. Especially when Paxton is getting ready to cut her eye off. (01:18:15)
Revealing mistake: Right after Kana opts for suicide by train, watch the security guard who starts running second from the left. He is having a hard time keeping a straight face and is obviously trying to hold off his laughter. (01:25:30)
Revealing mistake: When the lead character has his fingers cut off, you can tell the hand is just a prop, as it is completely motionless during the shot.
Revealing mistake: When the businessman has his fingers cut off by the lead character, you can tell the hand is a prop, as the skin tone does not match his hand in previous shots, and it moves unrealistically.
Revealing mistake: When the kids throw rocks at the bad guys, there is blood on his head before he is hit.
Answer: Exactly, yes. This interaction tells him that the police are in on the operation, and will not help him.