Continuity mistake: When Cliff is giving the kids their dinner, the pan cover keeps changing position.
Continuity mistake: The amount of water in Clair's cup changes a couple of times, most noticeably after Cliff tells her what she is eating, she takes a drink and the cup is about 1/3 full. She gets up to go find Theo, and now there is very little water in the glass.
Rudy's Sick - S1-E12
Continuity mistake: When Rudy is lying in her bed when Cliff is telling her about the germs in her body, her position on the bed changes between shots.
Mr. Fish (a.k.a. Goodbye, Mr. Fish) - S1-E2
Continuity mistake: During the scene when Cliff is explaining to Rudy that her fish is dead, the fish food disappears at one point then reappears.
Continuity mistake: At the end of this episode, when Clarie enters the kitchen and closes the doors behind her, they are left a bit open. They remain open while Vanessa and Dabnis also enter the kitchen to say goodbye. When they leave and Clarie asks Cliff something, the doors are now completely closed.
Waterworks - S4-E18
Continuity mistake: Rudy blows bubbles in her milk and the bubbles rise above the glass. The shot changes to Vanessa and when it goes back to Rudy the bubbles are gone.
Denise Kendall: Babysitter - S6-E6
Revealing mistake: When the power came back on and everything started running at once, the food processor was still running after the lid blew off of it.
Continuity mistake: There are two jackets hanging (one pink on top of one blue). When we see Vanessa and her friend, Janet, fighting Theo to get through the door, the pink jacket obviously falls down. When Dr. Huxtable comes in, the jacket is seen hung up again, but when he leaves, it is on the floor again.
Other mistake: When Denise and Rebecca are in the kitchen, Denise is playing a tape recording of the rap session from Uncle Wilton when they were doing the math rap. However, when Denise was attending the class, she never had a tape recorder, so there is no way she could have recorded anything.
Continuity mistake: When Vanessa and Dabnis are talking, Vanessa sits down and takes off her coat - it falls down behind her. For the rest of the scene the coat appears and disappears on the chair behind her.
Character mistake: When Dabnis and Vanessa first enter, Vanessa can be heard saying. "Hi, Grandpa. Hi, Rudy," when she is greeting Grandpa and Olivia.
Twinkle, Twinkle Little Star - S4-E15
Continuity mistake: In the opening scene, Vanessa pours a full glass of milk. In a shot a few seconds later, she is pouring the same glass about 1/4 full.
Character mistake: Rudy says that the last time some of Anna and Russell's friends visited them was during their 50th anniversary, and she got rich because they gave her money. In the actual episode of the Golden Anniversary however, the only guests at Anna and Russell's dinner party were the immediate family and Elvin.
Character mistake: Elvin has to sit on a stool at the dining room table and remarks that they are all out of chairs. But when Clair and Vanessa go into the kitchen to talk, there is an empty chair sitting by the kitchen table.
I'm `In' With the `In' Crowd - S6-E3
Continuity mistake: When Vanessa calls home and Denise picks up the phone, there is a cord attached to it. At first it's behind Denise's hand, then it's in front.
Plot hole: At the beginning of the episode, Theo, Vanessa and Rudy all act as if they forgot Clair's birthday. But Rudy already had a present for her mother's birthday, the pendant she ordered in the episode, "Cyranoise de Bergington".
Chosen answer: That is the song "Open the Door Richard."