Audio problem: Shaggy and Scooby are walking around trying to find the Ape Man to lure him into the trap. There is a sound and Shaggy says "What's that noise?" It cuts to Scooby who is following him who says "RI ron't row." But his mouth does not move at all when he says this. (00:14:15)
Continuity mistake: The Ape Man puts on a mask of Scooby and pretends to be a reflection. As he is mimicking Scooby's movements, he places his hand to Scooby's and his nails are sticking up. It cuts to a different angle and his hand is in a slightly different position, and his nails vanish. (00:10:05)
What a Night for a Knight - S1-E1
Plot hole: It seems unlikely that: 1. The curator, who's short and chubby could fit into that suit of armor. 2. How he could be strong enough to lift up the table Scooby and Shaggy are hiding under at one point, 3. That the museum has no security guards who might catch the curator and his thugs during their art forgery scheme and 4. There are eyes shown moving in the suit of armor when the gang's talking to the curator despite the fact he's the Black Knight Ghost.
What a Night for a Knight - S1-E1
Continuity mistake: Scooby's carrying the left shoe of the missing Professor White yet when they find him he's missing his right shoe.
Audio problem: Velma's voice comes out of Daphne's mouth at one point when they're scuba diving.
Continuity mistake: Shaggy's hair is briefly blond when the gang's scuba diving.
Scooby-Doo and a Mummy Too! - S1-E12
Plot hole: If the guilty man knew the diamond scarab was in the hippo statue then there's no reason he couldn't have broken the statue open and taken it.
Bedlam in the Big Top - S1-E10
Continuity mistake: The Ghost Clown's lips briefly turn light blue when he's hypnotizing Daphne.
Continuity mistake: The director's shown being outside the trailer in one shot after having been in the trailer before and after this shot when they're looking for the missing stuntman.
Continuity mistake: Carl, the stuntman, is shown barehanded in his trailer's trunk in one shot. When he says he's quitting he's suddenly got on ape gloves.
Mine Your Own Business - S1-E4
Continuity mistake: When Fred says that "I have a hunch that he'll turn up soon", there is a tape recorder on the desk and Daphne and Fred are standing in front of it, but in a close-up of the recorder, Daphne and Fred have gone.
Mine Your Own Business - S1-E4
Continuity mistake: When Scooby and Shaggy are standing at the closet doors, the door where is Shaggy is standing has the knob on the right hand side, but when the two swap places, Scooby opens the door and the knob is on the left hand side.
Mine Your Own Business - S1-E4
Continuity mistake: When Fred takes the map out of the body of the cigar store Indian, he is holding it with one hand, but in the next shot he is holding the map with both hands.
Mine Your Own Business - S1-E4
Continuity mistake: When Shaggy pushes Scooby into the abandoned hotel, there are two spots on Scooby's back, but after a quick cut to the gang standing outside the doorway, we return to Scooby and the two spots have disappeared.
Mine Your Own Business - S1-E4
Continuity mistake: When the gang opens the safe inside the old hotel, revealing the secret elevator, they are standing inside a large lobby, but when Daphne is attempting to coax into the elevator with Scooby Snacks, the lobby has gone and is now replaced by a wall.
Mine Your Own Business - S1-E4
Continuity mistake: Velma initially has nothing on her lips during the scene where Hank is showing the gang their rooms, but when Hank says "The Miner Forty-Niner", we cut back to Velma and Daphne and lipstick has now appeared on Velma's lips.
Mine Your Own Business - S1-E4
Continuity mistake: When Hank is showing the gang their rooms, Scooby has two dots on his back, one large and one small. Later on during the scene, the small dot has decreased in size.
Mine Your Own Business - S1-E4
Continuity mistake: When Fred asks Big Ben if he has any rooms available for the night, Daphne's eyes are drawn higher, drawn underneath her bangs, making her look off-model.
Mine Your Own Business - S1-E4
Continuity mistake: When Big Ben opens the door of the Gold City Guest Ranch, the door is red, but when we see Big Ben holding the door in the next shot, the door is now dark brown.
Mine Your Own Business - S1-E4
Continuity mistake: Daphne's scarf is green when she is sitting in the Mystery Machine, but when she with the gang at the entrance of the Gold City Guest Ranch, her scarf is now purple.
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.