Chihuahuas can shake or shiver for various reasons, including excitement, fear, cold temperatures, or illness. It's important to understand your Chihuahua's normal behavior so you can recognize when trembling is abnormal. Anxiety-related shaking is common in Chihuahuas and may be a sign of underlying conditions like separation anxiety or fear of thunderstorms. Trembling can also be caused by health problems, such as low blood sugar or organ failure. If your Chihuahua is shaking in cold weather, consider using a sweater. If trembling persists, it's important to see a veterinarian to determine the cause and proper treatment.