In the episode of Andy Griffith were he falls for Peggy MacMillan and Opie gets mad, there is a small slip up. At the very beginning, Opie and Andy are fishing Opie says that he got a fish, but his bobber is visible every now and then. There is nothing on it. This is in episode 64 season 3.
I couldn't add a new slip up because the cue was full, but it kinda fits here. In EVERY episode, during opening credits, Andy and Opie are headed to the fishing hole. Both are carrying fishing poles, but neither have a tacklebox, a bucket of worms, or any other form of bait.
This was production #64 (season3-episode 10) titled: Opie,s rival. You may need to rewatch this episode. At the beginning Opie and Andy are fishing,but the bobber is moving with a fish on it, same thing when they are in boat later with peggy. No error there.