While the boys create an advanced set of x-ray glasses, Candace finds a stray rabbit and adopts him. The rabbit, however, is Dennis, [[RogueAgent a former OWCA agent who went rogue]], and Perry must stop him before he causes trouble.

!! Tropes:

* AliensStealCattle: When Phineas looks inside a house with the x-ray glasses, he notices a group of aliens experimenting with a cow, causing it to levitate.
* ArtisticLicenseBiology: Dennis has pads on his feet, something real rabbits do not have.
* BaitAndSwitch: At the end of the episode, it appears that Major Monogram is going to give Perry a medal for defeating Dennis, but it turns out that he's actually swearing in Planty the Potted Plant as a member of the O.W.C.A..
* BalloonBelly:
** Dennis becomes massively obese after eating the entire truckload of carrots that fell into Perry's lair. Also doubles as ArtisticLicenseAnimalCare, since too many carrots are poisonous to rabbits.
** Buford also has one during the song "X-Ray Eyes"; when Phineas takes a look inside his belly, he sees an unrealistic amount of food inside as well as a "#1 Eater" ribbon.
* BitchInSheepsClothing: Dennis may seem cute, but in reality he's a mean RogueAgent.
* TheCameo: Linda only appears briefly in this episode when she sees "Mr. Cutie-Patootie" and figures that Candace got a new pet.
* ComplexityAddiction: Phineas offers to rescue Mrs. Garcia-Shapiro's wedding ring from the sink and asks Ferb to get [[NoodleImplements a blowtorch and a tub of mayonnaise]], but Mrs. Garcia-Shapiro instead wants to call her regular plumber, since he is bonded.
* CrazyPrepared: Since the glasses take hours to dry, Isabella puts them in her Quick-E Bake oven so they only take five minutes; as she states, "Fireside Girls are always prepared."
* CreatorCameo: The archaeologist who uses Phineas' x-ray glasses to dig for bones is Creator/JeffSwampyMarsh.
* CutenessProximity: Dennis when in pet mode looks undeniably adorable, which he uses to get Candace to take him inside the house.
* EpicFail: Doofenshmirtz has always been a HarmlessVillain, but him getting defeated by a ''fucking potted plant'' shows just how deep his ineptitude is.
* FoulBallPit: The boys use their x-ray goggles to look for and then fish out [[RecurringExtra Balthazar Horowitz]] from a ball pit.
* FreePrizeAtTheBottom: Phineas uses the x-ray goggles at the store to find the cereal box with the biggest prize (about as big as the box, in fact).
* FreezeFrameBonus: While waiting for Perry to arrive, Doofenshmirtz is reciting lines from a bound script book of things he'll say to Perry when he arrives thwart him for the day, and takes note to improve. While the middle paragraph is what he previously recited, the top paragraph are the stage directions for the episode (or rather describing the establishing shot of the Doofenshmirtz building), meaning he has the script of the episode itself.
* InanimateCompetitor: While Perry is away fighting Dennis, Doofenshmirtz puts a hat on a potted plant, naming it Planty the Potted Plant. Doofenshmirtz ties it up with a hanging rope and does his usual routine, as he does with Perry. He accidentally pushes Planty back, causing him to swing back and forth on the rope, repeatedly hitting Doofenshmirtz until he is forced to admit defeat.
* OOCIsSeriousBusiness: The normally upbeat and cheerful Phineas is offended when Candace calls the big idea "stupid".
* SelfDisposingVillain: Doofenshmirtz gets thwarted all by himself without Perry being involved at all (see InanimateCompetitor above).
* StartMyOwn: The boys decide to make their own x-ray glasses after ordering a pair of novelty x-ray glasses from a comic book that don't work.
* VisibleOdor: Apparently, the carrots' scent is so strong that they are represented by orange steam and catch the attention of Dennis. This is lampshaded by Baljeet in the character commentary.
-->'''Baljeet''': You know, you cannot see smell! I just want everyone to know that. It is not possible.
* WelcomeToMyWorld: Candace says this to Phineas after he turns away and an entire truckload of carrots disappears.
* WhatHappenedToTheMouse: Ferb and Isabella disappear from the third half of the episode on. We also don't know if the boys still have the glasses after the episode.
* WingdingEyes: Candace's eyes have hearts in them when she sees Dennis.
* XRayVision: The whole point of the MailOrderNovelty glasses the boys get. When it doesn't work, they decide to build their own.