General Tremors:
* ...leaf in a hurricane: Emphasizes the intensity and uncontrollable nature of the trembling.
* ...jellyfish in a storm: Highlights the fragility and vulnerability.
* ...twig in a strong wind: Emphasizes the weakness and susceptibility to fear.
* ...puppet on a string: Evokes a sense of being manipulated and helpless.
Specific Actions:
* ...newborn fawn in a hunter's sights: Captures the primal fear and helplessness.
* ...bird caught in a snare: Emphasizes the entrapment and desperation.
* ...rabbit caught in headlights: Highlights the immobilizing fear and inability to react.
* ...dog with its tail between its legs: Expresses a sense of shame and submission.
Metaphorical:
* ...candle flame in a draft: Emphasizes the fragility and vulnerability of their courage.
* ...castle built on sand: Highlights the instability and weakness of their resolve.
* ...glass sculpture in an earthquake: Emphasizes the potential for shattering and destruction.
The best simile will depend on the context and the specific emotion you want to evoke.