How are arguments passed to a function through __getattr__

Consider the following code example (python 2.7):

class Parent:
    def __init__(self, child):
        self.child = child

    def __getattr__(self, attr):
        print("Calling __getattr__: "+attr)
        if hasattr(self.child, attr):
            return getattr(self.child, attr)
        else:
            raise AttributeError(attr)

class Child:
    def make_statement(self, age=10):
        print("I am an instance of Child with age "+str(age))

kid = Child()
person = Parent(kid)

kid.make_statement(5)
person.make_statement(20)

it can be shown, that the function call person.make_statement(20) calls the Child.make_statement function through the Parent's __getattr__ function. In the __getattr__ function I can print out the attribute, before the corresponding function in the child instance is called. So far so clear.

But how is the argument of the call person.make_statement(20) passed through __getattr__? How am I able to print out the number '20' in my __getattr__ function?