When Lurch is sitting all alone on the chairs at the dance and the cowgirl walks up he thinks she's going to pick him to dance however she walks past him and takes the hand of the astronaut to dance with. But in the previous shot of the whole dance floor the astronaut was already dancing with someone.
When scratching Gomez' back, Thing is a left hand instead of the usual right. Thing is left again when he points Wednesday toward the play room to find Lurch.
Closing scene "his" and "her's". "Hers" is a feminine possessive pronoun. "Her's" is just wrong.
Gomez refers to Pugsley's pet as a toad. While the animal is popularly known as a horney toad or horn toad it is actually a lizard. There are 15 related species of horned lizard native to North America.