Why do sometimes changes to the "parent" prototype affect changes to the "child" prototype, and sometimes not?

Question

JavaScript

Why sometimes changes in the "parent" property prototypeof the constructor function affect the change in prototypethe instance object contained in __proto__, and sometimes not?

That is, here changes in the "parent" instance prototypedo not affect the "child" prototypeinstance in any way:

function Rabbit() {}
Rabbit.prototype = {
  eats: true
};

var rabbit = new Rabbit();

Rabbit.prototype = {};

alert( rabbit.eats ); //true - все работает без изменений

And here there is a change in the "parent" property - the "child" property changes:

function Rabbit(name) {}
Rabbit.prototype = {
  eats: true
};

var rabbit = new Rabbit();

Rabbit.prototype.eats = false;

alert( rabbit.eats ); //false - происходят изменения

Why is this happening? What is the logic of such behavior?