When Barney is reciting his incantation to ward off the jinx, two of the words he says are "hex" and "hexen," which are German for "witch" and "witches."
This is Clint Howard's first appearance on The Andy Griffith Show, as an uncredited boy at the church social (at 18 min 18 sec).
This black-and-white episode reveals that Opie has red hair and it isn't mentioned again.
At the very beginning of this episode, a couple walks past the barber shop and the man glances in the window. This exact scene was used at the very beginning of the previous episode, "The Manicurist."
It's well known that most of the large fishing and boating scenes were shot at Upper Franklin Reservoir in Franklin Canyon Park in Los Angeles, but this episode required a very shallow lake because the featured actors had to safely sink in their boat on camera. Just across Ballona Creek from the 40 Acres backlot, next to Jefferson Blvd, was a small 4' deep lake that was occasionally used in parts of early Tarzan movies. This solved the problem quickly and easily.