Wren

Tremors rather than writhing, head wobbling, stargazing where the head goes up and stays there, corkscrewing, and trouble righting herself. That last one matters with a hognose: the act ends with her flipping back over because to her mind dead snakes lie belly up. A snake that cannot right itself is not acting.

You have the distinguishing feature already and did not notice you had it: both times it happened when you picked her up. The display needs a trigger. Something startles her, she performs, and if you leave her alone she gets over it in a few minutes and goes back to being a snake.

The neurological version does not wait to be provoked. It happens while she is resting, with nothing done to her, and it keeps coming back. So the question is not what the movement looks like, it is what was happening in the thirty seconds before it started.