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The sketch has a running gag where Starlet's maid, Sissy, panics about things, until Starlet slaps her. The end of the sketch inverts this: After Rat leaves Starlet, she panics the same way Sissy did earlier, prompting Sissy to slap her.
Only appeared as a blooper years later, but still.. after the director told everyone time was short and not to goof around, Tim Conway proceeded to absolutely destroy a Mama's Family sketch by talking about a pair of Siamese elephants joined at their trunks, and the pathetic "hnorfl" noise they had to make instead of trumpeting. After Burnett desperately tried to get the show back on track by asking Vicki Lawrence in character to continue what she was saying, Lawrence replied, also in character, "You sure that little asshole's through?" Wave goodbye to any hope of recovering the sketch after that.
Once everyone had gotten that out of their system, they re-taped the whole thing again for broadcast. For comparison's sake, the full sketch as it actually aired can be seen here.
Though if this interview is anything to go by, the above story may be at least partly apocryphal. That being said, the story in that interview is at least equally funny, possibly more-so, than the above one.
The dentist sketch, with Tim Conway constantly giving himself accidental injections of Novocaine, and becoming more and more uncoordinated as a result. Made even more awesome by Harvey Korman becoming less and less able to hold himself together.