Addictive saliva

The door to the library opened, and the straight-haired young woman who had greeted me earlier entered the room. She gave me a passing glance, then walked past me, kneeling at Bianca's side. Rachel, I presumed.
Rachel murmured something too soft to hear, gently brushing Bianca's hair back from her face with one hand. Then she unbuttoned the sleeve of her blouse, rolled it up past her elbow, and pressed her wrist to Bianca's mouth.
I had a good view of what happened. Bianca's tongue flashed out, long and pink and sticky, smearing Rachel's wrist with shining saliva. Rachel shuddered at the touch, her breath coming quicker. Her nipples stiffened beneath the thin fabric of the blouse, and she let her head fall slowly backwards. Her eyes were glazed over with a narcotic languor, like a junkie who had just shot up.
Bianca's fangs extended and slashed open Rachel's pale, pretty skin. Blood welled. Bianca's tongue began to flash in and out, faster than could really be seen, lapping the blood up as quickly as it appeared. Her dark eyes were narrowed, distant. Rachel was gasping and moaning in pleasure, her entire body shivering.
I felt a little sick and withdrew step by step, not turning my back on the scene. Rachel toppled slowly to the floor, writhing her way toward unconsciousness with an evident glee. Bianca followed her down, unladylike now, a creature of bestial hunger. She crouched over the supine woman, and in the hunch of her pale shoulders I could see the batlike thing beneath the flesh mask, lapping up Rachel's blood.
I got out of there, fast, shutting the door behind me. My heart was hammering, too quickly. The scene with Rachel might have aroused me, if I hadn't seen what was underneath Bianca's mask. Instead, it only made me sick to my stomach, afraid. The woman had given herself to that thing, as quickly and as willingly as any woman to her lover.
The saliva, some part of me rationalized, desperate to latch on to something cold and logical and detached. The saliva was probably narcotic, perhaps even addictive. It would explain Rachel's behavior, the need to have more of her drug. But I wondered if Rachel would have been so eager, had she known Bianca's true face.
Now I understood why the White Council was so hard-nosed with vampires. If they could get that kind of control over a mortal, what would happen if they could get their hooks into a wizard? If they could addict a wizard to them as thoroughly as Bianca had the girl I'd just seen? Surely, it wasn't possible.

Storm Front Chapter 9, Page 110-111