[header] How to act like you're possessed [title] Become withdrawn, quiet and defensive. [step] One of the most tell-tale signs of demonic possession is a sudden change in personality. A usually happy and social person might become quiet and withdrawn, followed by negativity and hostility. 
Be very quiet and only speak when you are spoken to. [substeps] Reply in a monotone, emotionless voice and act defensively when you are asked any questions about your behavior.