This one is the misuse of “shaking one’s head” versus “nodding.” Lately, I have seen them used interchangeably so often.
Shaking one’s head means to move from side to side as in signaling a negative response to another person.
Nodding means to move one’s head up and down, signally an affirmative response.
This is one of those things which creates a disruption in the flow for a reader when the character nods, and you know she would be giving a negative response. This holds true for a character shaking her head when the reader knows it supposed to be a positive response.
In real life, I doubt any author nods when asked if they’re guilty of something they didn’t do. Nor do I believe they would shake their head if their agent asked if they want to accept a million- dollar contract with a publisher.
Just an observation.