Revealing mistake: When Eric Matthews is smashing his foot, he hits it the first time and it shows a close up. If you watch the small amount of blood when he hits it again they have used the same shot. (00:04:00)
Revealing mistake: During the "Rack" trap, look closely whenever there's a close-up of any of Timothy's hands or feet. It takes careful observation, but you can tell that many close-up shots have been horizontally flipped during editing. This was because the production only spent money on one prosthetic/prop hand and one prosthetic/prop foot for the twisting/bone-breaking effects, and in order to make it look like all four of his limbs were breaking, shots would be horizontally flipped. Thus the same prop/prosthetic could serve as both the left and right hand or foot. What gives it away is the blood pattern on the foot, which is perfectly mirrored between his two feet.
Revealing mistake: When Lynn is inspecting the "reverse bear trap", the trap Amanda was placed in for the first movie, you can see a small orange light reflecting off a few surfaces, like Lynn's arm and the nearby table. This is the brightness level auto-adjustment light that is present on many handheld cameras, which the cameraman apparently forgot to cover or turn off. (00:47:20)
Revealing mistake: Look at Matthews' toes as soon as he's done breaking his ankle, it's obvious that it's a fake foot. If you shine a flashlight through your toes, or fingers, it will shine most brightly through the edges of them because in the middle there's a bone to block the passage of light. The light shines right through Matthews' toes, and it's a solid color, obvious that there's nothing inside to block the passage of light. While he did break several bones in his foot to escape, it is unlikely that he took time to break his toes as there is no reason to, the shackle will slide off unbroken toes as well as broken ones. Also, even if he did break his toes, the broken pieces would still be in his foot and still block the light. It's a fake foot. (00:04:15)
Revealing mistake: During the "pig vat" sequence, as the pigs are being dropped into the grinder, in some of the shots from underneath the blades, you can see that the pigs are not falling directly into the blades, but rather, onto a sheet of glass right on top of them. (Look for the pigs to reflect in this glass.) (00:56:00)
Revealing mistake: After Tony rips his right hand from the chain you can see that the wound doesn't go all the way down to between his fingers, it stop about 1/2 an inch from the webbing of the fingers. The only way to get the chain out oh his hand was to completely rip it out between his fingers, the wound should have gone all the way out. (somewhat difficult to see, but just look carefully [slow-mo helps, but it NOT required to see this mistake]). (00:08:40)
Revealing mistake: Jeff tears a big chunk out of his face, but it never really bleeds out very much. It's pretty obvious that it's not just a layer of skin, you can see that there's a pretty big hunk of skin gone. At one point in the movie it's completely covered in blood, but only inside of the area of the tear. It should, at the very least, ooze quite a lot and drip something down his face, yet the area around the wound is always free from blood.
Revealing mistake: When Kerry is in the Angel trap there is a close up of her about to put her hand in the acid for the first time before it changes to a spinning shot. In the close up, watch very closely and you will see her fingertips enter the acid but she doesn't get burned or scream in pain. (00:15:40)