This is a video of some guys messing around in a 737 simulator. Starting at about 1:13, when they have the plane in a pretty deep stall, the attitude indicator degree markings no longer line up with the blue-and-brown horizon line. For instance, at 1:15, the markings indicate that the airplane is about 55 degrees below the horizon, but the horizon line itself is only about 20 degrees above the indicator.
So, which one is right? Is the plane 55 degrees or 20 degrees nose-down? And (most importantly) why would the attitude indicator give two conflicting indications like that?