(at around 1h 17 mins) When Officer Daniel Rigg arrives at the shop, the clock shows 1:16. But, at a second look, it's 3:46.
(at around 3 mins) During the autopsy the assistant weighs John's brain. When he removes the brain from the scale and walks away the dial on the scale does not go back to zero.
(at around 1 min) During the beginning autopsy scene, the person performing the autopsy puts his mask on upside down (the eye splash guard is at his neck). As soon as the camera jumps, the face guard is positioned correctly.
(at around 49 mins) Ivan's pierced eye changes from his left to his right and back to his left when the FBI Agents discover his body.
(at around 1h 1 min) When Agent Peter Strahm and Agent Lindsey Perez find the tape and the puppet in the school building, the tape recorder can be seen running before Agent Perez actually pushes the "play" button.
(at around 3 mins) During Jigsaw's autopsy, his brain is easily removed from the skull, with no connection to the brain stem or spinal cord. In reality, dissection is needed to remove the brain.
(at around 25 mins) Brenda's trap wouldn't scalp her in real life. The hair would rip and tear before the scalp would. Hair might be strong, but it's not that strong.
(at around 15 mins) When Officer Daniel Rigg is watching the interrogation video of Jigsaw's ex-wife he is looking at several books and magazines about Jigsaw. The book he picks up is titled "Jigsaw: Is He The Murderer The Police Say He His?"
(at around 5 mins) John somehow managed to swallow a tape coated in wax, which also worked perfectly.
(at around 54 mins) When Rigg approaches the door to the classroom, in which the husband and wife have experienced their trap, the painted red '?' on the door is still wet.
(at around 1h, unrated version only) Rigg pulls the last steel spike out of Morgan and Rex and drops it. However, the accompanying sound is that of a wooden rod landing on the floor.
(at around 48 mins) In the interrogation room a camera and a crew member is reflected in the two way mirror.
(at around 35 mins) Rigg is instructed to kidnap the motel manager for his test by using a pig head mask, which is pointless as the security cameras already knew he was inside the motel.
(at around 1h 8 mins) In a flashback, John Kramer is shown abducting Cecil Adams at a Chinese street festival celebrating the Year of the Pig. The last two years of the Pig were in 1995-1996 and 2007-2008. This does not match Jill's statement that these events took place shortly after John's diagnosis with cancer in 2003.
At the start John Kramer is in the morgue and the autopsy reveals he had swallowed a tape covered in wax that Lt. Mark Hoffman plays.
At the end John Kramer is still in the room where Agent Peter Strahm finds Jeff Denlon and shoots him, then Lt. Mark Hoffman locks Agent Peter Strahm in the room, so he could not of herd the tape at the start meant for him as John Kramer hadn't been found till the end of the film.
(at around 1h 4 mins) During one of the interrogation scenes a boom mic is visible in the reflection of the two way mirror.
(at around 25 mins) Officer Daniel Rigg tries to free Brenda by shooting the motor. Yet it never occurs to him that with her hair wound tightly into a ponytail all he had to do in order to free her was put the muzzle of his pistol right onto the ponytail and pull the trigger, the bullet would rip through her hair and she would be free.