Character mistake: Zeke makes the bold claim that "John Kramer didn't target cops." This is completely and utterly false, and a cop like him should know better. Kramer repeatedly targeted cops. In fact, both "Saw II" and "Saw IV" have officers (Detective Mathews and SWAT Commander Rigg) as Kramer's main target.
Character mistake: The prescribing doctor or a nurse should have given Matt/Joey's mom instructions on the proper use of an oxygen mask, but she did not demonstrate this. She picked up the mask, put it over her nose/mouth, and immediately inhaled ONCE followed by removing the mask. About a minute later, she repeated these ineffective steps. Instead of inhaling the oxygen, she was most likely simply inhaling "regular air" in the room - she did not keep the mask on long enough to enable release of oxygen.
Character mistake: Jean rolls, kneads, and flattens the dough a few times, repeating the steps to give the image of still preparing the dough. After the dough was flattened, it was well-shaped (round, higher, and more compact) then flat again. The way she was shaping the dough suggests she was making biscuits, but biscuit dough should not be handled that much (or the biscuits would be flat and not flaky). (00:18:00 - 00:19:00)