std::emplace_back invoking constructor of other objects in vector?

I am really confused about std::vector::emplace_back. I run the following code:

struct Thing {
    explicit Thing(std::string name) : name_{std::move(name)} {
        std::cout << "Constructed a thing called " << name_ << std::endl;
    }

    ~Thing() {
        std::cout << "Deconstructed a thing called " << name_ << std::endl;
    };
    std::string name_;
};


int main() {
    std::vector<Thing> things{Thing("A")};
    std::cout << "Size: " << things.size() << std::endl;
    things.emplace_back("B");
    std::cout << "Size: " << things.size() << std::endl;
}

and get this output:

Constructed a thing called A
Deconstructed a thing called A
Size: 1
Constructed a thing called B
Deconstructed a thing called A
Size: 2
Deconstructed a thing called A
Deconstructed a thing called B

Why on earth does things.emplace_back("B") invoke the deconstructor of the thing called A?