When is a reference an Rvalue reference?

I was playing with this example in order to understand rvalue references:

#include <string>
#include <iostream>
#include <utility>
#include <vector>

class Dog
{
public:
    Dog() {};
    Dog(Dog&& a) {  std::cout << "R value" << std::endl;}
};

Dog foo()
{
    return Dog();
}

int main()
{
    std::vector<Dog> v;
    v.push_back(Dog()); // calls move constructor

    Dog c(Dog()); // does not call move constructor
    Dog d(foo()); // does not call move constructor
}

I struggle to understand why in the line v.push_back(Dog()), object Dog() is treated as an Rvalue (so the move constructor is called), but the following two lines do not call move constructors. I guess I might be misunderstanding the relationship between an anonymous object and RValue here.