Has used physical cruelty or violence for the purpose of establishing dominance in a relationship (not merely to achieve some noninterpersonal goal, such as striking someone in order to rob him or her);
Is amused by, or takes pleasure in, the psychological or physical suffering of others (including animals)
This is actually what made me search for another cause in addition to NPD for her insanity. When she is hitting me, she actually lookshappy in some twisted, evil way. It's hard to describe it, but when she is doing something particularly hurtful (like choking and grabbing onto me to twist my arm/hand), her eyes get really wide and she almost looks like she's smiling, as though she is getting some satisfaction or pleasure out of it. When I fight her, I never feel any of those emotions, only anger and rage, so I'm sure I don't ever look like I'm "smiling" at all.