Bedlam in the Big Top - S1-E10
Revealing mistake: The clown's left leg goes through the solid wood floor of the wagon as he flies into it.
Bedlam in the Big Top - S1-E10
Revealing mistake: Velma climbs the ladder without her hands grasping the rungs.
Chosen answer: A ghost wouldn't have to keep any food in the fridge - they don't need to eat. So it is one thing that proves the ghost is not a ghost.