Unexpected behavior when passing derived class to base

#include <iostream>

class Shape {
public:
    virtual double getArea() const { return 0.0; }
};

class Rectangle : public Shape {
private:
    double width, height;
public:
    Rectangle(double w, double h) : width(w), height(h) {}
    double getArea() const override { return width * height; }
};

void processShapeObject(const Shape& shape) {
    std::cout << "Area: " << shape.getArea() << std::endl;
}

int main() {
    Shape shape;
    Rectangle rect(5, 10);
    processShapeObject(shape);
    processShapeObject(rect);
    return 0;
}