Visible crew/equipment: When evil Debbie Jellinsky is electrocuted, two stunt wires/cables are visible on her shoulders in the first close-up shot.
Revealing mistake: When they first arrive at camp and Joel goes to use his inhalers, the mouthpiece is actually in the storage position rather than the actuation position. The puff sound must have been added in later because the inhaler cannot be activated when it is put together that way. (00:22:20)
Answer: Michael Jackson was slated to record a song and music video for the film. The music video had him living in the Addams family mansion with angry townsfolk trying to drive him out of town for being scary and weird. The scene in the film was suppose to reflect that he scared "normal" kids, it had nothing to do with a scandal. When Evan Chandler started talking about his son being molested by Jackson, the song and music video were pulled and not included with the film. But the poster scene was left in. Later, when the scandal fully broke and more accusation were made, the joke of the scene took on another meaning.
Bishop73
Good thing the accusations were all false! :).