The English idiom “a one trick pony” means that a person is only good at one thing and probably repeats or shows you his or her one talent too often. This dead ringer is a play on that fact that monotheism is “a one trick pony” because YHWH is one, whereas + / – / 0 / ∞ / in / out is never “a one trick pony”. The dead ringer is also the fact that Adolf Hitler is riding a donkey or a pony into Jerusalem like Jesus Christ.