The way that Riki's girlfriend jumps off to her death changes before she hits the ground.
The way Oscar flies in two shots, while fighting Ricky.
Before the warden begins "hulking out" he seems very clearly takes off his belt. While he is hulking out, his belt is back on his pants before it snaps off. In fact, he actually removes his gun holster belt and puts it on the table before he "hulks out," and his belt around his pants snaps.
Obvious usage of dummy heads or faces for the violence.
Obvious dummy of Dan when he explodes from a gas-pressured bullet.
In a close up of Oscar grabbing his own intestines, the blood soaking onto his chest is clearly water-like and not thick.
When one of the guys has a meat cleaver swung to the face, the cut out piece is obviously visible before it hits the guy's face.
When Ricky punches the warden and sends him flying across the kitchen, the cable/wire holding him up is clearly visible.
When Ricky punches down the prison wall, the wires pulling the chunks of debris are clearly visible.