At the end of each episode of
Mystery Science Theater 3000 after the credits roll a short, 5 second clip of the
movie featured in the episode is shown. Typically the clip is the
oddest part of the
movie. This little clip is called "the stinger" by the show's creators,
Best Brains.
The first stinger appeared at the end of episode #205, Rocket Attack USA. Episode #207, Wild Rebels, did not feature a stinger. Fan speculation is that Best Brains simply forgot to add one. The stingers continued to appear at the end of the show until season 8, when episodes #805-807 (The Thing That Couldn't Die, The Undead, and Terror From The Year 5000) replaced the stingers with a clip of the Observers from the host segments holding their brains up to the camera. Episode #808, The She Creature, also did not feature a stinger. This time it was replaced with Professor Bobo (another host segment character) having fallen on to a planet.
Beginning with episode #809, I Was A Teenage Werewolf, the stingers returned and continued until the series finale, episode #1013 (Diabolik).
Furthermore, the stinger was missing from the Rhino Home Video release of episode #518, The Atomic Brain. Best Brains claims that the stinger was present on the master copy sent to Rhino, wheras Rhino claims it wasn't.
References:
http://www.mst3kinfo.com has everything a good MSTie could want.