When Amy was a rat, things were simple. A small cage, with not much to do but watch Willow watching Tara. Kissing Tara. Fucking Tara. So many positions, and if she could've thought in human terms, the sheer variety would've staggered her.
Now she's human again, and she doesn't know how to think. How to be.
Rack takes the choice away from her, and the ecstasy of mainlining pure power makes her writhe against the ceiling, as Willow writhes against her. Warm, willing, fluttering wetly around her fingers, and it's just another choice that isn't really a choice at all.