Warning - dangerous nerdery ahead!

[pmb]

def voodoo(f):
    def A(x):
        def B(y):
            return x(x)(y)
        return f(B)
    return A(A)

def hypothetical_fact(factorial):
    def f(n):
        if n == 0:
            return 1
        else:
            return n * factorial(n-1)
    return f

fact = voodoo(hypothetical_fact)

print fact(30)

The Z combinator is messed up. Anybody want to explain the above code to me?