Electric razor/bath scene

Among the things that puzzled me about this flick (mainly "why did i buy it?")is the scene where the older brother is torturing Stephanie's mother, in the bath. It's certainly strongly implied that he's raped her, but what's with the scene where he dangles the shaver in front of her? Is he threatening to drop it in the water and electrocute her? If so, then he never gets round to it. Or is he...ermm.. going to shave her downstairs bits or something? The meaning of this scene totally eludes me.