A Black Day for Mayberry - S4-E7
Plot hole: There is no reason for a gold truck from Denver to Fort Knox to be going through Mayberry.
A Black Day for Mayberry - S4-E7
Plot hole: About 2/3 through the show Barney is locked inside the armored car and Gomer puts about a gallon of gas into the gun port onto Barney's shoes. After Gomer is told of his error, Barney stays inside the truck. The fumes would have killed him, not to mention the risk of explosion.
Barney and the Cave Rescue - S4-E13
Plot hole: Andy and Helen go into the cave and there is a cave in. They find their way out and go into town to change, when they hear on the radio that Barney is getting the townsfolk together to form a rescue, Helen and Andy go back to the cave so barney can rescue them. This makes absolutely no sense. Once they get out of the cave why didn't they go back to tell Barney they were out, why did they have to flag down a truck for the ride back into town? Did they get to the cave with the squad car? It's hard to believe nobody saw them back in town, and how did they get to the cave?
Answer: It was a joke. They were supposed to be dumb hillbillies.
Both. According to later interviews with both Andy and the Dillards band (the real name of the band that played the parts of the Darling children, of which Charlene (Maggie Peterson - Mancuso was also a member) the reason the Darling boys never had any lines was because they would've had to have been paid if they spoke. In return for appearing without lines or pay, Andy promised to get as much of their music onto the show as possible which, he did. This obviously gave them a lot of exposure.