A Car object contains for Wheel objects. I have code that wants to find the circumference of all Wheels in my universe, calling get_circumference() to do so. ... If Car is marked as having the same fingerprint as Wheel, it will work.

But a car has four wheels? Surely $wheel->get_circumference and $car->get_circumference can't be doing the same thing so they don't have the same "fingerprint"?