Continuity mistake: Just before Shaggy goes into the secret passage way, he sits on a stone, and his hair has somehow turned yellow.
Continuity mistake: Shaggy's hair is briefly blond when the gang's scuba diving.
Continuity mistake: When the gang are in the Malt Shop at the end of the episode, Scooby puts straws together to steal Shaggy's drink, and succeeds until Shaggy cuts the straw. But after Velma says "That closes the mystery!", Scooby starts drinking through his straw and we cut to the other four drinks on the table. This time, Shaggy's glass is completely full.
Continuity mistake: When Daphne discovers the storehouse of scuba tanks, Fred is behind Velma and Shaggy. When we see Shaggy and Velma in the next shot, Fred disappears.
Continuity mistake: When Shaggy cannot light the match, he is holding a red matchbox in his left hand. In the next shot, the matchbox disappears.
Continuity mistake: Before Shaggy is about to light the fuse on the cannon, Scooby's tail is by the fuse. When we a close-up of the fuse, the tail has gone.
Continuity mistake: When Shaggy is sitting down after being squashed the door that Scooby opened, the door is closed. But when we see Shaggy in the next shot, the door is now open.
Continuity mistake: When Scooby inflates his diving suit, Shaggy punctures it and it leaves a hole on the right hand side of his diving suit. When Scooby trips up the ghost, the hole is now on the left hand side.
Continuity mistake: When Shaggy gets his foot caught in the rope tied to the bosun's chair, Scooby comes down on the chair and both he and Shaggy fall in the water. When they do, the rope and chair have disappeared.
Continuity mistake: When Shaggy grabs the bottle containing a message, his arm is bare, but before that he was wearing his long-sleeved diving suit.
Continuity mistake: When Fred says "That's where we'll find his ghost", Daphne is beside him. But after a quick cut to Scooby, we return to Fred and Daphne has disappeared.
Continuity mistake: When Velma is holding the glowing seaweed, the front cover of the book she is holding has nothing on it, but in the next shot the word "Biology" appears.
Continuity mistake: When Velma is speaking to Mrs Cutler, the background behind Mrs Cutler changes from a window to a staircase between shots.
Continuity mistake: When Velma is reading the book "Witchcraft Made Easy", the words are on the front cover. When she has the book under her arm, the words have gone.
Continuity mistake: When Scooby is fighting with the diving man's outfit, we cut to Fred, Shaggy and Daphne. But in the next shot Daphne is on her own and Fred and Shaggy have disappeared.
Continuity mistake: When Scooby is by the locker the door opens. When we see the diving man's outfit inside the cabinet in the next shot, the door is missing.
Continuity mistake: Scooby Doo is with the gang when Ebenezer Shark is speaking to them, but when we see Scooby a little later on, he is on his own with the gang nowhere in sight.
Continuity mistake: When the gang are speaking to Ebenezer Shark, look at Daphne and she is standing with her arm down her side. When we see Daphne in the next shot, she now has her hands on her hips.
Continuity mistake: When the gang are at the Malt Shop, on the table Fred and Velma's glasses are filled with milkshake. When Fred puts down the newspaper, both his and Velma's glasses are now empty.
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.
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.