Carlisle is a vampire, a pure predator and inhumanly fast and strong. Cell or not, River ought to be looking at least a little intimidated at that growl; there ought to be a flinch, however stifled, or a renewed light of wariness.

All she looks, though, is frustrated.

"That's the point," she says again, every word stressed. There's too much effort in her enunciation, as if she's working to say every word.

"Got the rules. Time to change it. Under the sensors."