Pesachim 110: Must We Believe in Demons?

Demons and pairs, or even numbers. Yes, this daf is esoteric for us. Why demons prefer pairs is unclear, though adding any second one to the Oneness of God may be part of the story. But the 4 cups is an even number! Why is that okay? The sages have an answer. Moreover, clearly, there is a range of opinions on the existence and power (or lack thereof) of demons. Plus: The story of a divorced man and his apparent complaint of witchcraft against him by his ex-wife that he was (temporarily) protected from by his own attention to pairs. Until he drinks too much - in an even number of drinks.