Phineas and Ferb try to find a way to make everything fun, starting with their house.
Meanwhile, it's Dr. Doofenshmirtz and Perry's 100th battle, and the O.W.C.A. has set up cameras all over Doofenshmirtz Evil Incorporated. Unbeknownst to either Doof or the O.W.C.A., Perry has accidentally been switched with an ordinary platypus from the zoo and is forced to go to the Charity Pet Wash with Candace and Jeremy.
"Misperceived Monotreme" contains examples of:
- Answer Cut: Candace takes Perry away to the Pet Wash before he can get to O.W.C.A. headquarters, prompting her to say "Will you stop squirming? You're a platypus; it's not like you have any place else to be." Cut to O.W.C.A. headquarters.
- Bait-and-Switch: Viewers are misled into thinking the regular platypus is going to defeat Doofenshmirtz after getting hit by the Least-Likelyinator, but this doesn't happen. It's Candace who gets hit.
- Bait-and-Switch Comment: When Major Monogram sees the ordinary platypus for the first time, it appears that he's going to realize that he's not the real Agent P... instead, he calls him out for not wearing his hat.
- Borrowed Catchphrase: Candace asks her brothers where Perry is. As soon as Phineas points to him, Candace says, "Oh, there you are, Perry", before he can get to his lair.
- The Cameo: Suzy and Jenny get a non-speaking one at the pet wash.
- Disney Acid Sequence: "Livin' in a Funhouse" is a musical number taking place in the surreal insides of of Phineas and Ferb's funhouse.
- Freeze-Frame Bonus: When the regular platypus knocks over the sandwich stand, for a moment it stands on its rear feet and its eyes are focused, like Perry when he is in agent mode. (This was most likely an animation error.)
- Hypocritical Humor: Linda suggests that Candace do some stuff instead of waiting around for Jeremy to call. Just as Candace insists she does stuff other than that, Jeremy calls her on the other line.
- Identical Twin ID Tag: The only thing that sets the normal platypus apart from Perry are its eyes, which are red instead of brown.
- Irony: Due to being hit with the Least-Likelyinator, Candace ends up being the one to clean up Phineas and Ferb's funhouse before she can show it to Linda.
- Leaning on the Furniture: When Irving gets zapped by the Least-Likely-inator, he suddenly has no interest in Phineas and Ferb, and attempts to hit on Isabella and reaches back as if he's trying to lean on a lamppost but falls over.Irving: There used to be a lamppost there.
- Metaphorgotten: "I see what you're doing! You're messing with my head, trying to get into my mind, walk around in there, rearrange the furniture, maybe repaint the kitchen..."
- Milestone Celebration: In-Universe. Monogram and Carl inform "Perry" (actually the platypus from the zoo mistaken for him) that he is about to fight his 100th battle with Doofenshmirtz, and to celebrate, they are going to watch him thanks to several hidden cameras placed in Doof's building.
- Mistaken Identity: Doofenshmirtz and Monogram mistake the platypus from the zoo for Perry and never realize the difference.
- Mythology Gag: When Monogram and Carl watch "Perry" and Doof's 100th fight, they sit under the OWCA logo that was created for this promotional image
◊. - Out-of-Character Moment: Invoked with Dr. Doofenshmirtz' latest inator, the "Least-Likelyinator." It forces the target to do something they'd never do normally, like making Irving uninterested in Phineas and Ferb's latest project (and try to hit on Isabella).
- Record Scratch: Perry's theme music is interrupted by a record scratch when Candace takes him to the Pet Wash.
- Red Eyes, Take Warning: Averted with the platypus from the zoo. It has red eyes so that it can be distinguished from Perry while he's in pet mode, but other than that it's just a regular platypus. However, Dr. Doofenshmirtz might tell you otherwise.
- Rhymes on a Dime: Multiple verses in the "Livin' in a Funhouse" number construct funny sentences for the sake of rhymes.
- Scooby-Dooby Doors: A variant occurs in "Livin' in a Funhouse", where the doors are placed on the walls, ceiling, and floor of a hallway, and every time Perry tries to open one, duplicates of him come out of all of them.
- Sdrawkcab Speech: When Candace cleans up the funhouse, the "Livin' in a Funhouse" song is played in reverse.
- Shout-Out: Dr. Doofenshmirtz is seen singing a parody of "Xanadu" by Olivia Newton-John, instead titled "Shangri-La".
- Singing in the Shower: Technically, the bathroom. One of the cameras in Doofenshmirtz's building caught footage of him singing in the bathroom with no shirt on, much to Major Monogram's amusement.
- Stunned Silence: When Perry finally reaches his lair, Major Monogram and Carl congratulate him on completing his 100th battle with Doofenshmirtz, even though he actually didn't. Of course, Perry can't talk, but his confused expression says it all.
- Tuckerization: Major Monogram refers to one of "Perry's" moves as the Marsh Maneuver.Major Monogram: I haven't seen one of those since 1974!
Carl: '74? You had a perm back then!
Major Monogram: Stay off the Internet, Carl! - Visible Odor: The smell of Carl's sandwich is visible. Major Monogram lampshades this:Major Monogram: Oh, for Pete's sake, I can see the smell from here!
- Visual Pun: Davy from the Navy whose hair is wavy literally has locks of hair shaped like little hands that are waving.
- Whatever Happened to the Mouse?: We never find out if the other platypus got back to the zoo.
