"Oh?" I bite my lip hard. "I'm glad my terror amuses them."
"Any idea which obstacle it was?" she asks.
"You're lying," she says. "You always bite the inside of your cheek when you lie. It's your tell."
I stop biting the inside of my cheek.
That's an actual piece of dialogue from the book. Now notice that in the first line, she bites her lip. Not her cheek. But then Christina accuses her of biting her cheek, and immediately she stops biting it.
I'm not quite sure where her lip became her cheek, but okaaaaay.....