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After getting busted on a DWI ("driving while intoxicated," not DOA ["dead on arrival"], as Chief Wiggum learned) charge[[note]]even though he passed the road test before Barney told the cops to give him a Breathylizer test, and Barney was never arrested either, since he drank even more than Homer did[[/note]] after sneaking out of work to go to a Duff Beer Factory tour, Marge urges Homer to go 30 days without beer. Meanwhile, Bart destroys Lisa's steroid-injected tomato and becomes an unwitting test subject in her new science fair project: "Is My Brother Dumber Than a Hamster?"

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!!Tropes featured:

* ActorAllusion: Lisa says she was chuckling over a joke from ''HermansHead''. Yeardley Smith was an actress on that show as well (even though she and fellow ''Simpsons'' voice actor HankAzaria don't like to acknowledge that they were on ''Herman's Head'').
* BedtimeBrainwashing: The episode opens with Principal Skinner awarding Bart first prize at the school science fair. The phrase "first prize" echoes until the scene transitions to reveal that Lisa was saying this into Bart's ear while he was dreaming because she was "just screwing with [his] mind."
* BrokenAesop: Invoked in-universe. An ad outside the Duff brewery says: "Friends don't let friends drive drunk" before it switches to a Duff ad depicting two friends drinking beer on the hood of a car. Homer putting this message into action also [[NoGoodDeedGoesUnpunished causes the episode's dilemma]].
* ComicBookTime: Ned says it's been 4,000 days since his last drink. 4,000 days is almost 11 years, but Ned makes it sound like his [[FelonyMisdemeanor bad event]] that made him join Alcoholics Anonymous only happened yesterday.
* CutenessProximity: Bart exploits this with his "Can hamsters fly planes" project. No one questions how relevant or scientific the project is because of the endearing diorama of a hamster in a toy plane.
* DeadBabyComedy: Chief Wiggum confusing DWI with DOA. Also Homer laughing at the montage of car wrecks (and Troy [=McClure's=] attempts to make jokes during it).
* FairWeatherFriend: Homer goes back to Moe's who is happy to welcome him despite badmouthing him the day before.
* ImagineSpot: Lisa has one where, thanks to her initial project, she's so famous that a family in Africa has a picture of her.
* IronicEcho: Skinner places Bart's project for "First Prize" as a result of a dream induced by Lisa. In reality, he ends up giving it to Bart as well, for an entry Bart made in reply to Lisa's humiliating project.
* KarmaHoudini: Barney gets away with essentially kicking off the episode's main plot by urging the police to give Homer a breathalyzer test right after he flawlessly passed a field sobriety test (granted, Homer beat Barney pretty bad in order to dissuade him from driving). After failing the breathalyzer test, the clearly sober-enough-to-drive Homer is arrested, stripped of his driver's license, forced to attend AA meetings, and gets into a bet in which he can't drink beer for a month; meanwhile, the obviously skunk-drunk Barney is allowed to drive off, even knocking one of the cops off a cliff as he speeds away.
** Bart zigzags this after destroying Lisa's science fair project. When Lisa actually attempts to make him suffer some form of retribution (and gets him to repeatedly [[TooDumbToLive self inflict pain and humiliation onto himself]] in the process), he responds by ''winning the science fair!''
** YMMV. What Bart did was bad but Lisa's retribution was pretty mean spirited (it basically boils down to her embarrassing him in front of the entire school). Neither kid comes off as the clear "good guy" in the episode.
* LaserGuidedKarma: Wiggum arrests the still relatively sober Homer, and allows the very clearly drunk Barney to drive home without doing any tests on him. He's immediately knocked off the road by Barney and sent rolling into a tree before [[StuffBlowingUp inexplicably blowing up]].
* LeaningOnTheFourthWall: At the end of the episode, when Homer leaves Moe's bar to go on a bike ride with Marge, Moe proclaims "You'll be back. And so will all of you, and you... and ''you''," whilst looking and pointing directly at the viewer, [[FourthWallPsych before quickly cutting to a different shot to show he was talking to Barney]].
* MadeOfExplodium: Chief Wiggum's beer-stein costume. (He's OK after the commercial break.)
* MadeOfIron: In order to prevent him from driving drunk, Homer punches Barney in the face, clubs him with a crowbar, and slams the car door on his head five times to no effect.
* OnlySmartPeopleMayPass: Bart hides Lisa's report and dares her to find it by deciphering a fiendish series of clues...only for Lisa to find it before he's finished gloating.
* ScrewThisImOuttaHere: A woman shows up at the Police Station and tells Chief Wiggum she's there because someone called and said her husband was found DWI. Realizing it's another of his usual DOA / DWI mixups, Wiggum directs her to other cops and leaves.
* StatusQuoIsGod: Anyone who is vaguely familiar with the Simpsons knows that Homer's sobriety is short lived (he's back the drinking the next episode). It dampens the heartwarming ending on rewatch.
* TakeOurWordForIt: Obviously, we do not see the multitude of car crashes in the film that Homer and his AA class watch. We can still imagine the horror of it all, given the sounds of the crashes (the offensive SoundtrackDissonance aside) and the reactions of the class (which range from shock, disgust and fear, save for [[JerkAss Homer]], who finds it funny since [[NoSympathy he doesn't know any of the victims.]])
* YoungerThanHeLooks: Hans Moleman is revealed to be 31 years old and looks old because of severe alcoholism. Before anyone cries "NegativeContinuity!", this does tie in with the birth date on his driver's license, as seen in "Selma's Choice," which is August 2, 1961 (which would make him around 31 to 32 years old at the time of this episode's premiere).