Candace decides to help Jeremy at a construction site, blowing off her spa day plans with Stacy. Phineas and Ferb also build their own spa back home. Meanwhile, Doofenshmirtz adopts a stray cat, which causes trouble for him.
Tropes:
- Big "OMG!": Candace and Stacy react to the sight of Phineas and Ferb's home spa with an "Oh... my... gosh..."
- Brick Joke: About halfway through the episode, Dr. Doofenshmirtz says he's nicknamed Carl the intern "Dr. Coconut", and then admits Perry doesn't want to know where that nickname came from. The Stinger has Carl putting a coconut bra and grass skirt on over his clothes, along with an otolaryngologist's mirror, and practicing hula dancing.
- Butt-Monkey: For a change of pace, Stacy takes on the role of victim of circumstance at the construction site while Candace keeps fawning over Jeremy.
- Continuity Nod: The kitty Doofenshmirtz adopted messes around with some of his inators, most notably his Gloom-inator (from "Leave the Busting to Us!") and Media-Erase-inator (from "Voyage to the Bottom of Buford"). Also returning from the latter episode is the giant squid that Buford fought, seen in this episode fighting with Buford over some seaweed.
- Cute Kitten: Mr. Fluffypants. His appearance gives Dr. Doofenshmirtz the opportunity to rescue him and Pet the Dog, though he gradually grows more frustrated as Mr. Fluffypants keeps setting off his Inators.
- A Day in the Limelight: The A-plot is mostly centered on Candace.
- Disney Acid Sequence: The "Spa Day" song.
- Don't Explain the Joke: Doofenshmirtz has nicknames for all his friends and enemies. His nickname for Major Monogram is Monobrow; Doof quickly realizes that his joke wasn't as funny as he thought it was.
- For Inconvenience, Press "1": Played with. When Candace tries to pull Stacy aside with Jeremy next to them, she imitates an Interactive Voice Response system, saying "Please hold" and "Your call is very important to us" each time Jeremy interrupts.
- Formally-Named Pet: Dr. Doofenshmirtz adopts a kitten he names Mr. Fluffypants, after his Uncle Fluffypants who, oddly enough, never wore pants.
- Fun with Homophones: Phineas says making a spa would give them a chance to show off Ferb's seaweed wrap. Cue Ferb beat-boxing, indicating it's actually a seaweed rap. Sure enough, the "Spa Day" song features Ferb busting out some rap verses.
- Gesundheit: Said in the "Spa Day" song after the word "shiatsu" is mentioned.
- Golden Moment: Parodied; when Candace tries to give an apologetic monologue with a Sentimental Music Cue, Stacy interrupts her by saying "You sound like one of those TV shows we like to make fun of."
- Knows a Guy Who Knows a Guy: How Candace and Stacy were able to get a reservation for the spa.Candace: Well, I know Stacy...
Stacy: And I know this neighbor who knows this hair-washer who knows this bank teller who knows this back waxer that works at the spa.
Candace: Yeah, and I know Stacy. - Lame Rhyme Dodge: Jeremy overhears Candace say "spa day", to which she responds, "You heard 'spa day'? Because I said 'hurrah day'! Like, 'Hurrah, I can't wait to build houses!'".
- Mistaken for Stray: Mr. Fluffypants, the cat that Doofenshmirtz finds outside his building and believes to be a stray cat. At the end of the episode, the owner finds Dr. Doofenshmirtz with the cat, whose real name is simply "Mr. Cat." He reluctantly returns the cat to its true owner.
- Noodle Incident: Stacy forgives Candace for making them miss their spa day, saying it makes them even for that time in the third grade when Stacy glued a hamster to Candace's hair to impress Billy Clark.
- Pet the Dog: Played with. After Perry saves Doofenshmirtz and Mr. Fluffypants, a boy comes up and tells Doofenshmirtz that Mr. Fluffypants is actually his family's cat. Doofenshmirtz looks at the camera and says, "Ah, I'm going to have to do the right thing here aren't I? Fine, here you go." Doofenshmirtz returns the cat to the boy as a crowd of onlookers says "Aww!".Doofenshmirtz: Don't you people have jobs?!?
- Record Needle Scratch: When Stacy stops Candace's apologetic monologue.
- Start My Own: Since Phineas and Ferb don't have enough connections to get into the spa, they decide to build their own spa instead.
- Subverted Catchphrase: Isabella approaches Candace and Stacy and asks them, "Where ya goin'?" in the same intonation as "Whatcha doin'?"
- Title Drop: By Candace and Stacy at the beginning when the title card coincidentally appears. Also multiple times throughout.
- Underwater Fart Gag: Implied when Buford is shown sitting in a bubbling hot tub and he says, "It's not plugged in".
- A Wild Rapper Appears!: An extreme example. The song "Spa Day" starts out as a smooth, Bossa nova song a la "The Girl From Ipanema", but then transitions abruptly into a rap.
