Audio problem: Velma's voice comes out of Daphne's mouth at one point when they're scuba diving.
Audio problem: When the gang (except Fred) talk about unloading the Mystery Machine, there are no lip movements whatsoever.
Mine Your Own Business - S1-E4
Audio problem: When we see the gang in the Mystery Machine at the beginning of the episode, we hear Fred and Shaggy speaking, but their mouths are not moving.
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)
A Gaggle of Galloping Ghosts - S1-E11
Audio problem: The Frankenstein monster growls like the werewolf at one point in the laboratory.
Jeepers It's the Creeper - S2-E3
Audio problem: When the gang are driving in the Mystery Machine at the end of the episode, Fred says "Well, now that we're rid of the Creeper, " but his mouth is not moving.
The Haunted House Hang-Up - S2-E5
Audio problem: When Fred says "Is this your ghost, guys?", his mouth does not move.
The Haunted House Hang-Up - S2-E5
Audio problem: When we see the Mystery Machine at the end of the episode, we hear Daphne's voice but her mouth is not moving.
The Haunted House Hang-Up - S2-E5
Audio problem: In a shot of the Mystery Machine at the beginning of the episode, Fred says "I wish I could find some kind of groovy road sign to tell us where we are", but his mouth is not moving.
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.