Fly On the Wall

Buford removes a part from a tire swing the boys are building and it accidentally shoots a ray that turns Candace into a fly. Meanwhile, Doofenshmirtz is suffering from evil scientist’s block.

Songs

 * Summer (Where Do We Begin?)
 * Fly on the Wall

Perry's entrance to his lair
Perry goes down the basement staircase, stopping at the landing next to the Panic Room, opens the bottom stair, stops himself halfway down after forgetting his hat, retrieves it from the stairs, and goes back down into his lair.

Background Information

 * The kids unintentionally reference the events from "Phineas and Ferb The Movie: Across the 2nd Dimension" when Buford, Baljeet, and Isabella start singing Summer (Where Do We Begin?). Phineas then says "We all know this song...I don't know how...", confirming that they didn't have their memory of the events of that day back.
 * Doofenshmirtz breaks the fourth wall in this episode, explaining that he and Perry have been battling each other for four years, a nod to the fact that this was the first episode produced for Season 4, as well as the length of the series' run.
 * This episode reveals that Bobbi Fabulous wears a wig.
 * It is revealed that Dr. Doofenshmirtz has an uncle named Boris.

Errors

 * In the song, a scene pops up of a calender on June. It folds back a month, but it shows a July calender. It should have shown May.
 * It's unknown how Buford, Baljeet, and Isabella know the song, "Summer (Where do We Begin?)", because they were not even with Phineas and Ferb when they were singing that song.

Continuity

 * This is the second episode to feature a character being turned into a fly. In "Picture This", Buford accidentally got mixed with a fly in Phineas and Ferb's machine.
 * Seventh time Candace spends most of the episode after being changed by an invention. ("Does This Duckbill Make Me Look Fat?", "Attack of the 50 Foot Sister", "Split Personality", "Canderemy", "Excaliferb", "Doofapus")
 * Candace is seen as a praying mantis ("Candace Loses Her Head") and changes into the Giant Floating Baby Head at one point.

Allusions

 * The Fly - Candace gets turned into a fly much like what happens to the main character in the story. The line "Help me, help me" from the 1958 film adaptation is also used.
 * The Son of Man - Doofenshmirtz's painting is inspired by this 1964 self-portrait by René Magritte, depicting the artist with an apple obscuring his head.

Cast

 * Vincent Martella as Phineas
 * Ashley Tisdale as Candace
 * Thomas Sangster as Ferb
 * Caroline Rhea as Mom
 * Mitchel Musso as Jeremy
 * Dan Povenmire as Dr. Doofenshmirtz
 * Jeff "Swampy" Marsh as Major Monogram
 * Tyler Mann as Carl
 * Richard O'Brien as Dad
 * Dee Bradley Baker as Perry
 * Martin Olson as Human Head Fly
 * Tiffany Espensen as Ginger Hirano
 * Additional voices:

- Did not appear in this episode.