Christmas with the Addams Family - S2-E15
Other mistake: As Morticia starts to play the flute, Gomez appears to have been filmed backwards, his hair and suit is reversed.
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.
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