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.
Christmas with the Addams Family - S2-E15
Continuity mistake: When the second Santa (Grandma) knocks at the children's door, in one brief shot Wednesday already has 2 dolls in her arms.
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.
The Great Treasure Hunt - S2-E19
Visible crew/equipment: When Morticia bounces the anchor on the floor, the wire used to make it bounce is visible when she puts it down.
Happy Birthday, Grandma Frump - S2-E22
Continuity mistake: As Morticia and Gomez play with the train, there is only one train on the set. When Gomez blows it up at the bridge, there is a second train in the midst of it. This is a reuse of stock footage.
Visible crew/equipment: As Mr. Hinson and his aide get out of the car, the shadow of the boom mic is visible on the house.
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