DP: Don't say that -- some kid is going to go out, dig a tunnel and have a cave-in.

JM: We built go-karts or bicycles; we were always out doing something. We wanted to capture that imagination.

Sister Candace (l) tested well with girls. Viewers responded positively when she gets her comeuppance.

Much to her endless frustration, sister Candace is unable to prove to their mother what Phineas and Ferb are up to, as evidence of their activities perpetually vanishes moments before mom arrives. Meanwhile, and unbeknownst to all, the boys' pet platypus Perry is actually suave Secret Agent P, engaged in perpetual battle against arch-enemy Dr. Doofenshmirtz. The three separate elements of each story regularly intersect in unexpected ways.

JM: The show has a level of plot complexity they won't let most people do.

DP: That was actually the reason it didn't get picked up until now. Fox Kids wanted to put it on their next season; we had a couple of meetings with them. At Nickelodeon it kept going up higher and higher to the next echelon. Everyone loved it, but they eventually thought it was too complex to pull off. Disney was the first to say, "Let's see if you can do it in 11 minutes." We did it in the pilot and they said, "Let's see if you can do it for 26 episodes."

In one episode, Phineas and Ferb beat boredom by building the best roller coaster ever in their backyard. Before they know it, they and the neighborhood kids are on a wild ride throughout the city and the universe.

JM: I think it's great that the characters are cool, edgy and clever without the humor being mean-spirited. It was important to us that they never did anything with any animosity. They never tried to get their sister in trouble or outsmart their mother and get away with it.

DP: We were trying to do that and still keep an edge to it. Our animation director Rob Hughes moved back from Michigan because he liked the pilot so much he wanted to work on the series. He said on all the other shows every character is either stupid or a jerk, but there are no stupid characters or jerks in this one.

JM: Except the creators.

DP: Candace does get frustrated. She thinks it's not fair -- that if she were doing the things they're doing, she'd get in trouble. It's not, "I'm going to get those guys and ruin their lives." She does bust them later in the season, but there are a couple of twists to it.

Strangely enough, the show tested just as well with girls as boys. In some age groups it tested a little higher with girls -- they love it when Candace gets pounded, boys and girls alike.

JM: Girls would definitely like to see her take more abuse; we're gonna take their notes and, boy, are they lucky. They also like Perry -- they say he's "hunky."

DP: His adventures often clean up the boys' mess. When we were writing Rocko, we always had one of two things, sometimes both: usually a song or a musical number, plus a big action/chase scene. Phineas and Ferb gave us a chance to write a song for every single episode, starting with the second episode, Flop Starz.

Phineas and Ferb decide to surprise Candace for her birthday by carving her face alongside the presidents on Mount Rushmore. The producers aim for their characters to be cool and edgy without being mean-spirited.

We played it and Perry's [secret agent] theme for the Disney executives. We were a little trepidatious because Disney has a big history of music -- what if they hate it? The reaction was, "These are great -- can you write a song for every episode?"

JM: We both want to be rock-and-rollers anyway -- Dan's had a band for years, and I was in one once.

DP: Every episode since then has song in it. It's not always the characters singing onscreen -- they don't break into song just to advance the plot. The music doesn't come out of nowhere, sometimes it's just a montage over action. We've done every genre known to man: ABBA, Broadway show tunes, 16th-century madrigals --