- 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 and uses inedible things to make it. Plankton sees that as useless, so he goes to the audio system. Before that, 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.
Plankton does not want to hear that, so goes to the command central: the brain. When he goes inside, he is basically 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, he becomes yellow with lime spots (holes), grows two buck teeth and eight fingers, and somehow, brown pants, black shoes, a red tie, and a white shirt are on him.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 somehow brings him home, but not before bumping into Patrick.
Once accidentally sucking up info from Patrick, Plankton becomes pink, chubby, stubby-armed, one-toothed, grows the swim trunks Patrick wears, and forgets the formula. Once Plankton is back at the Chum Bucket, Karen asks him what the formula is. Plankton acts like an idiot since he forgot the formula after turning into Patrick.
|( ‣ ) Associated production music|
|( • ) Original music|
|( ◦ ) SpongeBob music|
‣ Secret Agent SquarePants - Nicolas Carr [title card]
‣ Charivari Clowns (a) - 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]
‣ Cartoon Sting 2 - Plankton in Spongebob
‣ Sailor's Sting 4 - 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 [SpongeBob bursts into Krabs' office]
‣ 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 Hawaiian Sting (l) - SpongeBob laughs
‣ Steel Sting (c) - 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 10 - 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 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 slight obesity.
- 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 was the last episode to premiere during Nickelodeon's 1984-2009 Splat era.
- 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 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.