When Amanda and Daniel entered the bathroom from 'Saw', Adam's body is shown with his right leg shackled. However, in 'Saw' and in Amanda's flashback in 'Saw III', his left leg is shackled.
When Jigsaw and Eric escape the lair via a hidden elevator, the low-budget of the film prevented the construction of an actual working elevator. Thus, some tricky photography and editing was implemented. For the first shot where we see Jigsaw and Eric "going down", the scene was simply shot by raising the camera vertically to give the impression of them "going down" on an elevator. For the next wide shot, simple digital effects were added to make it appear that the room was "lowering." And for the final shot, where we see the top of the elevator going down an elevator shaft, stock footage from the film "Hollow Man" was used.