- Karen Plankton
- Sheldon J. Plankton
- Hamster (debut)
- Frankie Billy
- Monroe Timmy
- Squidward Tentacles
- Patrick Star
- SpongeBob SquarePants
- Abigail Marge
- Nancy Suzy Fish (cameo)
- Nat Peterson
- Fred (blue)
- Eugene H. Krabs
- Brain Gary (debut)
Plankton tries to steal the Krabby Patty secret formula, with Karen launching him into Mr. Krabs' brain, but ends up going into SpongeBob's brain instead, which Karen and Plankton did not know SpongeBob was holding a cardboard cutout of Mr. Krabs until he moved it away.Plankton goes into the optical system to see how to make Krabby Patties, but SpongeBob cannot see because of Plankton and uses inedible things as ingredients. Plankton doesn't realize this until he decides to go the audio system to listen to the formula, restoring SpongeBob's sight. SpongeBob thinks he forgot to make the Krabby Patty, so he asks Mr. Krabs to tell him the secret recipe again, but by the time he gets in front of him, Plankton is already using SpongeBob's eardrums. SpongeBob cannot hear Mr. Krabs, so the latter repeats himself by yelling, then by using a megaphone. This blasts Plankton away and SpongeBob regains his hearing with him and Mr. Krabs forgetting the reason for his visit.
Plankton then tries to go to the command central, the brain, to learn about the formula. When he goes inside, he is in SpongeBob's pineapple but spaghetti-ish and pinkish, so he goes into the library. He looks at SpongeBob's secrets and finds that the formula is in the heart. He slides the vertebrae down there and when he sucks information from SpongeBob's heart, his appearance changes to SpongeBob's body and wears SpongeBob's clothes.Plankton then acts like SpongeBob when Karen calls out to him, asking him if he got the Krabby Patty recipe yet, to which Plankton responds that getting the formula is stealing. Karen brings him home, but bumps into Patrick.
Plankton then accidentally sucks information from Patrick, causing him to have the appearance of Patrick's body, wears Patrick's clothes, and forgets the formula. Once Plankton is back at the Chum Bucket, Karen asks him what the formula is, but Plankton has no idea and acts like Patrick.
|( ‣ ) Associated production music|
|( • ) Original music|
|( ◦ ) SpongeBob music|
‣ Charivari Clowns - Daniel Jean Jeannin [Plankton watching TV]
‣ Cartoon Sting 1 - "Hey, I was watching that!"
‣ Vibe Q Sting - Nicolas Carr [two people enter]
‣ Background Blues - Otto Sieben [they're visiting the most disgusting places in town]
‣ Steel Sting - Jeremy Wakefield [Plankton sighs]
‣ Shadow Villain - Meyer Kupferman [Karen telling Plankton how to get the formula]
‣ Danger HQ - Norman Dane ["Prepare for launch."]
‣ Armed Attack - Jean Clero [Plankton launched toward Krusty Krab/Plankton gets inside SpongeBob]
‣ Noodly Shenanigans - Nicolas Carr, Barry Anthony [Plankton sees what SpongeBob does]
‣ Jovial Pirates Jig - Michael Bolger, Nicolas Carr ["Order number 17?"]
‣ Mission Improbable - Nicolas Carr, Barry Anthony ["That's it! I'm trying something else."]
‣ Nude Sting - Nicolas Carr [SpongeBob screams]
‣ Drama Link (g) - Hubert Clifford ["Mr. Krabs, help me, Mr. Krabs!"]
‣ Mission Improbable - Nicolas Carr, Barry Anthony [Plankton goes to SpongeBob's eardrum]
‣ Sailor's Sting 12 - Michael Bolger, Nicolas Carr ["Need a little refresher, eh?"]
‣ International Intrigue - Joe Sherman [Plankton unplugs SpongeBob's eardrum]
‣ Sailor's Sting 12 - Michael Bolger, Nicolas Carr [SpongeBob can't hear Mr. Krabs]
‣ Evil Mind 8 - Dick de Benedictis ["Here it comes!"]
‣ Sailor's Sting 12 - Michael Bolger, Nicolas Carr [Krabs using a megaphone]
‣ Finger of Fear - Fredric Bayco [Plankton goes to SpongeBob's brain]
‣ Vibe Sting - Nicolas Carr ["Why am I making idiotic comments?"]
‣ Lap Steel - Nicolas Carr ["Superficial greetings?"]
‣ Tension Bits - Nicolas Carr, Sage Guyton, Jeremy Wakefield ["Personal opinions? Knock-knock jokes?"]
‣ Drama Link (d) - Hubert Clifford [Plankton goes in deeper]
‣ Moon Walk - John Fox [inside SpongeBob's brain]
‣ Vibe Sting - Nicolas Carr ["Sounds that make Squidward upset?!"]
‣ Unknown Track 96 - SpongeBob laughs
‣ Steel Licks (i) - Jeremy Wakefield ["Patrick's favorite places to be scratched?!"]
‣ Zelle 501 - Gerhard Trede [the secret recipe's located in the heart]
‣ Striptease A - Peter Fallowell [Plankton's mouth watering]
‣ Straight from Hell - Gregor F. Narholz ["All of the ingredients coming together in perfect harmony!"]
‣ Drama Link (c) - Hubert Clifford ["Okay, that was weird."]
‣ Frankenstein's Niece A - Gregor F. Narholz [Plankton transforming into SpongeBob]
‣ Skipping to School - Sage Guyton, Jeremy Wakefield ["It's beautiful!"]
‣ Tales from the Swamp (a) - Ron Goodwin [Plankton transforming into Patrick]
‣ Twelfth Street Rag - Sage Guyton, Jeremy Wakefield [ending]
- As of November 15, 2017, The Internet Movie Database (IMDB) gives this episode a rating of 6.5/10/10 based on 0 ratings by users. TV.com users give this episode a rating of 5.7/10 based on 9 votes.
- This is the second episode where Plankton goes inside of SpongeBob's head. The first was "Plankton!" He does it again in The SpongeBob Movie: Sponge Out of Water, but it won't be the same as next time.
- However, in this episode, SpongeBob's brain is bigger than it was before.
- When Plankton looks like Patrick, he appears to have an increased weight to show Patrick's obesity.
- It may or may not be a coincidence, but both this episode and its sister episode, "Someone's in the Kitchen with Sandy," involve Plankton trying to steal the formula in some way.
- This is the second episode in which Plankton tries to ruin the Krusty Krab without anyone noticing him, the first being "Banned in Bikini Bottom," where he revealed the Secret Krusty Krab to Mrs. Gristlepuss and the entire police force. The third is "Frozen Face-Off."
- This episode premiered on the same day as nine other episodes, which notably includes "Goo Goo Gas" from season 5. This means that two episodes with a two-season gap premiered on the same day.
- This episode premiered two years before "Drive Thru" would premiere, eight years before "Sold!" and "Lame and Fortune" would air in Greece, and nine years before "High Sea Diving" and "Bottle Burglars" would first air in Russia.
- This is the first episode to use Moon Walk since "Squidtastic Voyage." Coincidentally, both episodes have similar plots, and they're played during similar scenes.
- This episode has a highly similar plot to Plankton!-Plankton invades SpongeBob's brain to steal the formula, while in Plankton!, he uses mind-control.
- This was the last episode to premiere during Nickelodeon's 1984-2009 Splat era.
- When SpongeBob screams as he notices the Sponge Patty he unknowingly made, his teeth are yellow for a split second.
- When Patrick walks out of the Krusty Krab, after Karen takes Plankton, Patrick's animation freezes for one second.
- Just as Plankton completes his transformation into SpongeBob, his eyelashes are missing for a split second.
- SpongeBob cannot hear if his eardrum is not plugged into a wire. However, when Plankton detaches his plunger from his eardrum, SpongeBob could hear again despite the fact that his eardrum was not plugged in again.
- Patrick's lips are pink when he leaves the Krusty Krab.
- Plankton is seen sliding down SpongeBob's spine. However, SpongeBob should not have a spine, because sponges are invertebrates. A similar mistake was made in "Roller Cowards" and "Mermaid Man vs. SpongeBob."
- SpongeBob's heart is not shown beating.
- In this episode, SpongeBob has an eardrum, but in "Blackened Sponge," Frank says that sponges don't have eardrums.