If a living being is still, can it start moving without something external acting on it?

Answer 1

It can move its body parts relative to the rest of its body with no external force acting. However, to start its body moving relative to something else it needs an external force. This can be a reaction force, as when the being pushes down to lift its weight and receives an upward force, or pushes a mass of air backward in flying and gets a forward thrust, etc. It can also be a force originated externally, such as a shove, wind force or gravity.