Continuity mistake: When Shaggy is sitting down on the beach, the umbrella behind him is blue. When he runs into the umbrella a little later on, it is now coloured red.
What a Night for a Knight - S1-E1
Continuity mistake: When Daphne suggests leaving the painting room through another door, the Black Knight appears and you can see he has red crest of hair on his helmet. But after a quick cut, we return to the gang and the crest on his helmet is missing. It re-appears when he comes to the painting that Shaggy is hiding behind.
What a Night for a Knight - S1-E1
Continuity mistake: When Scooby sees the Black Knight, he throws up the bones and they form a skeleton of a dinosaur. When we see a close-up of Scooby in the next shot, the dinosaur skeleton is nowhere to be seen.
Don't Fool With a Phantom - S2-E8
Continuity mistake: When the Wax Phantom closes the door, you can see the door latch does not have a lock, but in the next shot a lock appears on the door frame.
The Haunted House Hang-Up - S2-E5
Continuity mistake: When Scooby Doo and the gang are pursued by the invisible ghost with a candle, they hide in a room and Scooby blows out the candle and shuts the door. You can see the door has a handle on the left hand side, but when we see the gang in the room in the next shot, there is no handle on the door.
The Haunted House Hang-Up - S2-E5
Continuity mistake: When Shaggy lifts the rug to discourage the headless spectre, it looks like it goes back into place. But when Velma, Shaggy and Scooby Doo are chased down the stairs by the spectre a little later on, the rug is nowhere to be seen.
The Haunted House Hang-Up - S2-E5
Continuity mistake: When Fred attempts to open the door, there is no keyhole under the door handle. But in a close-up of the handle in the next shot, a keyhole appears.
Bedlam in the Big Top - S1-E10
Continuity mistake: Velma throws the umbrella to Scooby pointed end first, but when it arrives at Scooby, the umbrella is handle-end first.
Bedlam in the Big Top - S1-E10
Continuity mistake: After the umbrella turns inside out, Scooby loses his grip with the umbrella and falls to the trampoline, but the umbrella does not follow Scooby down.
Bedlam in the Big Top - S1-E10
Continuity mistake: The table behind Shaggy changes color several times as he performs the Lion Tamer act in the cage with the lion.
What a Night for a Knight - S1-E1
Continuity mistake: When Velma loses her glasses, the Black Knight trips over her and lands on the guillotine. She mistakes the Black Knight's growls for Shaggy's sore throat, and pours some cough mixture on to a spoon. When Shaggy enters and runs up to Velma, she is wearing her glasses again.
What a Night for a Knight - S1-E1
Continuity mistake: When Velma says "What a spooky place!" to Scooby, you can see Velma is standing by Scooby but in the next shot she has disappeared.
What a Night for a Knight - S1-E1
Continuity mistake: When Scooby is guarding the door, it is open. When he stops, it is open, and in the shot after that, the door is closed again.
What a Night for a Knight - S1-E1
Continuity mistake: When the gang arrive at the Museum, you can see the handle on the Rear Entrance door is on the left hand side. When Shaggy opens the door and lets Fred, Daphne and Velma in, the handle is now on the right.
What a Night for a Knight - S1-E1
Continuity mistake: When Shaggy puts the ladder on the wall near the Museum Rear Entrance, you can Fred is standing by an open door of the Mystery Machine. In the next shot, he is now standing near Shaggy.
What a Night for a Knight - S1-E1
Continuity mistake: When the gang say "Professor Hyde White!" in the library, you can see Shaggy has his hand on Fred's shoulder. When we Fred and Velma in the next shot, he doesn't.
What a Night for a Knight - S1-E1
Continuity mistake: When the gang are driving along in the Mystery Machine, you can see Velma is sitting by the window. When we see a full view of the front seat, she is now sitting between Shaggy and Daphne.
What a Night for a Knight - S1-E1
Continuity mistake: When Mr Wickles is standing by the crate containing the Black Knight armour, you can see the lid is resting on it. But in a close-up of Mr Wickles, the lid is missing.
What a Night for a Knight - S1-E1
Continuity mistake: When the gang discover an empty suit of Black Knight armour in the truck, you can see the helmet is beside the wheel. When Daphne notices a piece of paper by the wheel, the helmet is nowhere to be seen.
What a Night for a Knight - S1-E1
Continuity mistake: When we see the truck at the beginning of the episode, you can see that the label on the crate is completely clear. When the Black Knight opens the crate, the label now has writing on it.
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.