- Gary the Snail
- SpongeBob SquarePants
- SpongeSnail (debut)
- Patrick Star
- Squidward Tentacles
- SquidSnail (debut)
- Scooter (cameo on bus)
- Fred (mentioned)
- Other jellyfishers
- Dr. Gill Gilliam (debut)
- Clam (mentioned)
- King Neptune (mentioned)
SpongeBob and Patrick are all set to leave for the Jellyfishing Convention in Ukulele Bottom that weekend. Realizing that he will not be able to take Gary, SpongeBob leaves Gary in Squidward's responsibility.
SpongeBob takes Squidward around his house, telling him that he will have to feed Gary for three days. There are very large cans of snail food with the words "morning," "afternoon" and "night" written on them so that Squidward will be able to keep track. Eager to get rid of both of them, Squidward lies and says that he will do it to get SpongeBob and Patrick to leave. They do, and Squidward runs out of SpongeBob's house and sits in a lounge chair for the whole weekend, thus ignoring Gary. He soaks up plenty of sun, but Gary is left in the house, looking longingly in the direction where SpongeBob left, horribly neglected.
When SpongeBob gets back, Squidward suddenly remembers that he was supposed to take care of Gary. However, when he goes to get to the snail, he finds him very sick, due to lack of food, water, and attention. Squidward, thinking he will be able to help, tries to give Gary some food. However, Gary is so weak from waiting for SpongeBob to come home, he is limp in Squidward's arms and will not eat. Squidward puts Gary down as he hears SpongeBob and Patrick saying goodbye to each other and tries to force feed Gary. When he hears SpongeBob coming in, Squidward gives up and puts all of Gary's food into his mouth. He greets SpongeBob awkwardly and explains that he was only checking on Gary.
Just as Squidward is about to leave with a smirk on his face, Gary slowly enters the room. SpongeBob realizes that something is wrong, and quickly calls the local veterinarian, Dr. Gill Gilliam. He comes over to SpongeBob's house and gives SpongeBob a syringe full of snail plasma. SpongeBob asks Squidward to give Gary the plasma, as he is squeamish. Squidward reluctantly agrees and, while trying to inject Gary, accidentally injects SpongeBob with snail plasma causing SpongeBob to worry about the consequences. Upon realizing that Gary only needed water, Squidward leaves telling SpongeBob not to worry because he's fine after SpongeBob tells Squidward what's gonna happen to him now that is injected with snail plasma. Sometime later, SpongeBob starts acting slow and somewhat like a snail, as well as eating Gary's food himself after SpongeBob thinks that he's fine like Squidward had said. When he goes to the bathroom, his eyes stretch out of his body and grow, his body becomes flat to the ground, his arms and legs disappear into his body, his body reshapes itself, and he also loses the ability to talk after saying "Something is wrong with meeeeeeeeeow!". As a finished result, SpongeBob has turned into a snail, becoming SpongeSnail.
Afterwards, he goes over to Squidward's house to get help, but Squidward is terrified of the fact that SpongeBob turned into a snail because of his lousy aim and he throws the snail plasma away and he tries to reassure himself, but he hears SpongeSnail at the door and starts blocking the doors and windows and tries to run and hide from SpongeSnail as he realizes that he should've taken care of Gary and none of this would ever have happened if he had. SpongeSnail chases him for help, but Squidward keeps running for his life, thinking he's under attack which ultimately makes a mess of his house. Amongst the chaos, Squidward accidentally injects himself with the plasma, turning him into a snail as well, becoming SquidSnail.
The ending has Gary, SpongeSnail, and SquidSnail meowing to the tune of "Blow the Man Down" on top of a fence. Patrick, who has been awakened and annoyed by this, yells at them to clam up and throws a boot at SquidSnail, knocking him off the fence. Gary and SpongeSnail continue to meow, but SquidSnail tries to meow. The episode ends after fading to black.
|( ‣ ) Associated production music|
|( • ) Original music|
|( ◦ ) SpongeBob music|
‣ Honolulu March - Hans Haider [opening]
‣ Aloha - Dick Stephen Walter [the next morning]
‣ The Achterhoek Dances - Jan Rap [Squidward at the door]
‣ Me for You - George Callert [Squidward not listening to SpongeBob]
‣ Cream Pie - Sage Guyton, Jeremy Wakefield [bus arrives]
‣ On the Beach - Kapono Beamer [Squidward sunbathing]
‣ Grass Skirt Chase - Sage Guyton, Jeremy Wakefield [Squidward tries to feed Gary]
‣ Funeral March - Peter Lea-Cox [Gary's sick]
‣ Dramatic Impact 5 - Ivor Slaney [SpongeBob screams]
‣ Woe is Me! - Richard Myhill ["Squidward, something's wrong with Gary!"]
‣ On the Beach - Kapono Beamer [snail plasma]
‣ Cello Link (a) - Dick Stephen Walter [Gary coughs]
‣ Gator - Steve Belfer [Squidward tries to give Gary the plasma]
‣ Dream Sequence - Dave Hewson ["I don't know, I feel kind of funny."]
‣ Hawaiian Holiday - Kapono Beamer ["He just needed water?"]
‣ Twelfth Street Rag - Sage Guyton, Jeremy Wakefield [SpongeBob eating snail food]
‣ Curse of Evil 1 - Gregor F. Narholz [SpongeBob transforming into a snail]
‣ Esta Noche A - Hans Ehrlinger [Squidward in bed]
‣ House of Horror - W. Merrick Farran [SnailBob at Squidward's door]
‣ Hawaiian Link (a) - Richard Myhill [The moon shines]
• SpongeBob ScaredyPants - The Ghastly Ones [closing credits]
- This episode is available on the Halloween, Complete 1st Season, First 100 Episodes, The Complete First Season, Holidays with SpongeBob 3-DVD Gift Set, The First & Second Seasons, Movies & TV Collection, The Best 200 Episodes Ever, and Karate Choppers DVDs.
- This episode is also available on the Halloween (VHS) tape.
- "I Was a Teenage Gary" was ranked #41 during the Best Day Ever event on November 9–10, 2006.
- This episode premiered in Canada on October 30, 2000.
- Squidward does not seem to recognize Gary in this episode, even though he interacts with him in "Culture Shock" when he introduces Gary to the audience.
- This means this possibly takes place before that episode.
- The aftermath of Snail SpongeBob chasing Squidward leaves the latter's house a mess with the wreckage including a portrait of Squidward destroyed by the end of his clarinet.
- Coincidentally, the snail plasma item is caught on Squidward's nose a few seconds afterward.
- This is the second time Squidward enters SpongeBob's house, the first was in "Nature Pants."
- Despite this, in "Squid's Visit," he claims he's never entered SpongeBob's house before, meaning this takes place afterwards.
- There was a rumor that in the original airing, there was a scene showing Squidward's transformation to a snail. Although, it has been proven to be fake.
- As of June 12, 2016, the deleted scene was confirmed to have been false by a YouTube user named 90sGiveMeGoosebumps, who has a tape with the original airing of this episode. In fact, as further proof, he also uploaded a clip of All That cast member Lori Beth Denberg introducing this episode as brand new.
- The so-called deleted scene was never drawn in the storyboard of this episode.
- The song that Gary, SpongeBob, and Squidward meow is "Blow the Man Down," which is what the show's theme song is based on.
- In the console version of the Lights, Camera, Pants! video game, there is an art gallery with a painting that is based on this episode.
- This is the first episode to have a time card to mark how long time has gone by.
- However, the French Narrator does not pronounce it like he does in later episodes.
- In the Filipino dub, a narrator does pronounce the time card, albeit in English.
- However, the French Narrator does not pronounce it like he does in later episodes.
- This is the first episode in which Gary plays a major role.
- This was Steve Fonti's last time working on SpongeBob SquarePants.
- This was also Chris Mitchell's last episode until season 4 episode "Mermaid Man and Barnacle Boy VI: The Motion Picture," and his last as a storyboard artist.
- In the Latin Spanish dub, the episode name is "Un buen vecino", which translates to "A good neightbor."
- In the Polish dub, the episode's title is "Ślimaczy weekend," which translates to "The Snail Weekend."
- In the Croatian dub, the episode name is "Kad sam bio Slavko," which translates to "When I was Gary."
- In the Japanese dub, the episode name is 「ガリーの病気」, which translates to "Sick Gary." This does not make any reference to the snail transformations.
- "3 Days Later..."
- The title of this episode is a reference to the 1957 classic horror movie I Was a Teenage Werewolf, which was riffed on the cult classic show Mystery Science Theater 3000.
- When SpongeBob's arm falls off, he says "It's okay, I'm a lefty anyway" despite the fact that it is his left hand that falls off.
- Squidward throws the snail plasma earlier in the episode and it makes a breaking sound. However, it is perfectly fine at the end of the episode, as he is injected with it.
- When SpongeBob plays fetch with Gary, there is a watch on his arm, but when Gary returns the fetch toy back to SpongeBob, it is gone permanently for the rest of the episode.
- When SpongeBob says "What a great friend you are, Squidward," the closed-captions read, "You're a great friend, Squidward."
- When Squidward says "Eat! Eat! Eat! You've gotta finish this food!," Gary lip syncs to what Squidward was saying.
- In this episode, the snails are seen sitting on a wooden fence. However, there are no fences near Conch Street.
- When Gary returnes with the ball, the exercise wheel is no longer there.
- When Patrick smashes the wall, the fish that was on it disappears.