Diana Ross - S4-E23
Continuity mistake: When Diana Ross finishes her first song, the bird has both his feet on the ground; in the next shot, the bird has one leg raised, without enough time passing to do so. (00:08:45)
The Robbery - S4-E4
Plot hole: Towards the end, Jake (Shirley's boyfriend), hangs the girls on a coat rack by the hoods of their coats. They try a few comical ways of trying to escape, when they could have simply unbuttoned their coats and slip away.
Revealing mistake: The opening scene was shot twice, complete with a rear-end automobile collision in the foreground for both takes. The initial collision destroyed the taillights of the first car and the headlights of the second car and ruptured the second car's radiator on impact, spilling its contents into the street. The production crew attempted to sweep away the debris with a broom before the scene was reshot. If you examine the roadway before the two cars appear in this scene, you will see a prominent splatter on the pavement that has been swept with a broom almost precisely where the cars impact again moments later.
Continuity mistake: When Mat knocks out the door, which falls on Pat and squeezes him, he uses a hand pump to inflate him. After Pat comes to life, the hand pump disappears.