Or the One Where
Homer's half brother Herb reappears and invents a baby translator. AKA the one with the vibrating chair.
After a routine physical shows that Homer is sterile due to years of working at the nuclear power plant, he is awarded the First Annual Montgomery Burns Award for Outstanding Achievement in the Field of Excellence in order to disguise the $2,000 settlement he receives from Mr. Burns. The sudden windfall attracts the attention of Homer's estranged, derelict half brother Herb.
Obviously, this episode is a sequel to season two's "Oh Brother, Where Art Thou?" which introduced Homer's half brother Herb. Danny DeVito reprises his role as Herb, though curiously, this is the last we'll see of the character. Reportedly, DeVito was not terribly excited about recording this episode, so perhaps he's simply never expressed any further interest in returning.
This episode aired in August, well after the show's third season ended, because Fox ordered an extra episode at the last minute to air over the summer. It is generally considered part of the third season, and appears in that season's DVD set.
Homer's view of the world while sitting on the vibrating chair is a reference to 2001: A Space Odyssey. The presence of the chair in the episode was inspired by a similar chair one of the writers bought while working long hours to complete the episode.
Boxer Joe Frazier voices himself in this episode, presenting the Excellence Award to Homer.
Lisa: This show is the biggest farce I ever saw!
Bart: What about the Emmys?
Lisa: I stand corrected.
Homer: There's an empty spot I've always had inside me. I tried to fill it with family, religion, community service, but those were dead ends. I think this chair is the answer.
Bart: I think we should get a machine gun. We can use it to hunt game, spell out things, or ring in the New Year!
Homer: All right, Herb. I'll give you the money, but first you have to forgive me and treat me like a brother.
Homer: All right, then just give me the drinking bird.
For whatever the reason, this episode always feels big. Maybe it's because it originally aired during the summer, giving it a "special episode" aura that lingers to this day. Or maybe it's the return of one of The Simpsons' few guest stars with limited appearances. Or Homer's winning of the First Annual Montgomery Burns Award for Outstanding Achievement in the Field of Excellence and a rare financial windfall for the family. Or that vibrating chair gag everyone remembers. Whatever the reason, this episode feels like a finale, in an ephemeral, hard-to-explain kind of way, and it sends the third season of The Simpsons out on a strong note, a season which set a new bar for quality that will be met and exceeded in the seasons to come.
The return of Uncle Herb closes out a season which saw The Simpsons reach new heights.