It is stated that one of the characters is a serial killer and you see him kill 2 of his victims, but they're a lot more he has killed just 2 are shown.

He kills both of the people in the same manner, by poisoning them and removing they're 2 front teeth. You see the men get poisoned, they struggle and grasp their throats, but you do not see the killer remove their teeth. This was probably done to keep the rating under R.

For G*d's sake

None.

Nothing

The simple fact that one of the characters is a serial killer might upset children and the overall tone of the movie is quite bleak.