Also the demon in the novel and the first film says that “we are quite a little family in here” or words to that effect. Also the demon takes on the persona of the dead Burke Dennings. Merrin says that there is only one invading personality, but that doesn’t stop the demon from pretending to be “legion”. “The parties” expelled “from the body of a child” are the Gemini’s continuation of the demon’s deception that there are multiple possessing personalities.