The Doctor: You know when grown-ups tell you everything is going to be fine and you think they're probably lying to make you feel better?
Amelia: (rolls eyes) Yes.
The Doctor: Everything's going to be fine.
Tattletale: Okay, well, imagine that this woman got powers that let her turn into something so wrong that she's got some sort of mental block that keeps her from transforming if anyone can see. Maybe because she's so ashamed of being seen like that. When nobody's looking, though, she's a monster. Lightning-fast and all sharp.
Tattletale: Not even remotely close to the truth. But it's the best I can offer you. Don't take your eyes off her.