Homer: I'll never wiggle my bare butt in public again.

Lisa: I'd like to believe that this time, I really would.

Episodes revolving around Homer and Lisa's up-and-down relationship are another staple of the series:

We've found those two such a good contrast for each other -- Lisa's intellectualism vs. Homer's dumbism play off each other so well that we do write a lot of stories around them -- you're gonna get one of those a year. It's kind of like Laurel and Hardy in that they complement and contrast each other so well.

Kirkland views The Simpsons as a parody of what we see in life and there are always new ideas for the writers to parody.

Principal Skinner: I'd like to bid farewell to our students who are graduating, or going off to fight in Gulf War Five: Operation Find Our President's Head.

Kids: USA! Find the head! USA! Find the head!

Fantasy-premise episodes, once restricted to the annual 'Treehouse of Horror' show have become more common in recent years, as the writers seek to expand the show's canvas beyond the well-explored confines of its internal reality with fables and stories set in the future:

We usually do one or two a season, apart from the Halloween show. I love them personally, but they're challenging to do. On the artwork level, every design is a new design, which means a lot of research. The director and assistant director have to watch to make sure the design is consistent within the episode. We have our standard model sheets, everyone knows how to draw Homer. But when you have Homer as a Frenchman in the 18th century, then all eyes are on that model sheet.

There are three segments in those half-hours, and each segment is art directed differently. Those costume pieces are always a visual challenge, as are the effects. Last year we had ships tossed around at sea. It's amazing how the writers keep raising the bar for the directors and animators. They're more apt to say 'we can do anything, this is animation.' They'll challenge us to draw whatever they picture.

The Simpsons is a combination of the whimsical and the intellectual, yet some of the funniest laughs come from low comedy. Kirkland likens it to The Three Stooges as written by Bernard Shaw. © 2003 FOX.

What I love about the show is the combination of the whimsical, there's an intellectual side to the show, and yet some of the funniest laughs we get are the low comedy laughs -- Homer running around with a plunger stuck on his head. It's funny in kind of a Three Stooges way, but it's The Three Stooges written by Bernard Shaw.

Lisa: Oedipus is the one who killed his father and married his mother.

Homer: Arrghh! Who paid for that wedding?

Lisa: At this rate, I'm gonna end up at Vassar.

Homer: I've had just about enough of this Vassar bashing, young lady!

There's intellectualness to our writing and we credit our writers. They're extremely intelligent. My intellect feels pretty small sitting in with our writers because they're so sharp. You go into our writing room and they're reading the Wall Street Journal or the New Yorker. They're just up on everything.

In addition to Hollywood actors and rock stars, celebrity authors (Michael Chabon, Tom Wolfe), artists (Jasper Johns) and even an architect (Frank Gehry) have lent their voices to The Simpsons; at this point, Hawking probably qualifies as a series regular.

The [celebrities] are approached. Somehow you find out so and so's a fan. What often happens, as in George Harrison's case, he did it because his son Dhani loves the show. A lot of times the celebrities do it because of their kids. It's become a roast, because if they sign up they know they're going to be made fun of, but it's a healthy fun.