Continuity mistake: When Rudy comes down the stairs and wants a lemon, Cliff is cutting one. In one shot it is fully cut. He givers her a piece of one he had cut earlier. When Rudy leaves suddenly he has a uncut lemon in front of him that he cuts.
Continuity mistake: After Clair turns off the record, the folder on the table changes position.
Continuity mistake: When Theo puts the phone down, the handset cord is next to the phone. The next shot it is now under the phone, when the phone rings it is now next to the phone again.
The Dentist - S2-E16
Continuity mistake: The amount of orange juice in Cliff's cup changes - you see him filling his cup, the next shot it is almost empty, a couple of shots later it is now full again.
Continuity mistake: The amount of milk in Robert's glass changes a few times throughout the scene in the kitchen.
Continuity mistake: At the very end of the episode Clair's glass is suddenly fuller after Denise gets done singing.
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.
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.
Chosen answer: That is the song "Open the Door Richard."