Continuity mistake: The air hoses at the end of the film keep changing position. There is a shot from above: the air hoses are below actually resting on top of the glass box. Then when Strahm is trying to get out through the roof, there is a small rectangle cut out of the grated mesh and the hoses are above the roof and are not resting on the box anymore.
Continuity mistake: The tape recorder changes position in the final game. After the walls start moving in, Strahm drops the tape recorder and it is facing the door, completely straight. When he goes and gets his gun to shoot the box, it is on a slant now. Strahm didn't move it.
Continuity mistake: Spoiler: Right at the end, we find out that Saw III and Saw IV were happening simultaneously, as demonstrated by Strahm walking in and killing Jeff. We then see Hoffman close the door on Strahm, locking him in the room. Saw V continues from the exact moment when Hoffman shuts the door on Strahm. In Saw V, Strahm quickly kicks the door with his foot just seconds after Hoffman has closed it. However in Saw IV, we see Hoffman walking away. In this shot we should hear Strahm kicking on the door.
Continuity mistake: In the beginning of the movie, Strahm reaches out into the hall to grab the tape player. The string it is hanging from comes with it. Strahm exits the room, and we get a reverse angle and the string that held the tape player is hanging from the ceiling, but empty. The string should not be there to begin with.
Chosen answer: Assuming the woman in the bathtub was able to be moved safely the amount of blood gained from her, while still being helpful, would probably not be enough to save the final two survivors from self harm. Without the heart pumping blood you would only get the blood that was in her arm at the moment. You would have to lift her or raise her so gravity would get other blood moving to get enough. Which the final two possibly could have done, but stress of the situation clouded their judgement.