Christmas with the Addams Family - S2-E15
Revealing mistake: When Morticia is playing the flute, the strings that operate the basket lid and rope are visible.
The Great Treasure Hunt - S2-E19
Revealing mistake: When Fester gives the anchor to Morticia, she drops it, and it bounces back up. When she lays it down, the wire used to achieve the gag is easily seen.
Revealing mistake: As Fester looks at the mirror, it shatters. After he asks a question, it falls off the wall. After it does, you can see what appears to be someone's fingers pushing from the other side to knock the mirror down. That spot on the wall is obviously fabric covering a hole.
Revealing mistake: In the wide shots of the car, the camera side of the sound stage is reflected in the car's finish.
Answer: Basically from what I understand, they stuck the innards of a small flashlight into the base of the bulb and put a little switch on it. When he put it in his mouth and bit down, his teeth would hit the switch, which would turn on the flashlight and made the bulb light up.
TedStixon