A Gaggle of Galloping Ghosts - S1-E11
Continuity mistake: The Frankenstein monster suddenly appears outside the pantry door after Scooby opens the door - the monster did not walk out, but just appeared.
A Gaggle of Galloping Ghosts - S1-E11
Continuity mistake: In the Mystery Machine, Daphne is seated close to Fred, but the next shot shows her alone.
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.