P's earring disappears and reappears throughout her argument with Joe over the gun.
At the beginning of the final chapter, the Molotov cocktail Joe throws at the car envelops the entire vehicle. When the shot cuts to Joe walking away, the car behind her is only partially aflame. The scene ends with a closeup of the car burning exactly as it was in the first shot.
The "eight cylinder car", as Joe refers to it during her staged breakdown, is a twelve cylinder Jaguar Sovereign. However, some engine bay shots show Jaguar's XK6 straight-six engine when the script needs the ignition cables to be messed with. This is presumably on account of the cables being way easier to access on the straight-six than on the V12.
In the director's cut, during the opening of the chapter The Mirror, after Seligman explains that the top of the diamond is called a mirror in some languages and Joe mentions he has a mirror on the wall, you can clearly see the camera and crew members reflected in it. You even see the camera move as it pans right.