Start with a resting pose and choose one unexpected event in the scene. Sketch how the character might react using its whole body rather than only its face.
Try this
A paper boat may tilt when a raindrop lands nearby. Compare a small tilt with a large one and ask which matches the tone of the story.
Take it further
Consider what happens just before and after the reaction. Adding those two poses gives the surprise a context and can make the action easier to follow.
