What causes a dog to tremble and shiver?

Answer 1

Usually they shake or tremble when they are anxious. Some dogs tremble when riding in the car, others when they hear thunder. Some dogs are very insecure and would benefit from wearing a compression garment, like a thundershirt.

Answer 2

The dog if it shakes is under a acceding amount of stress, or is nervous.

Answer 3

It scared, cold or sick. Also, some dogs shiver when they need to go to the bathroom really badly.