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: This is actually a reference to both Eli Roth and Quentin Tarantino's experience with the same hooker. After both Tarantino and Roth "had" the same call girl without either of them knowing, the hooker replied to both of them as she left their separate rooms, "I get a lot of money for you, and that makes you MY bitch. Hence, the opening line for the trailer. Both of them had a big laugh during the premiere.