When Morticia climbs onto her turned around chair, pretending it's a balcony, the spider tassels are missing from the bottom of her dress.
When Lurch tells Gomez and Morticia that Cousin Itt and Uncle Fester are both gone, he is not looking directly at them. It then cuts to a different angle, and he is facing them.
Early in the episode as the camera shows Thing and scans across the room, you can see the backside of the person who is supplying the hand for a brief moment.
Morticia mispronounces timbre as timber; the vowel sound in the first syllable is different.