[The episode starts with scallops flying and chirping.]

Squidward: [exits his house] What a sun-tastic day! [slips on Gary's snail trail] Snail trail. [Gary looks through a window as Squidward mops up the trail] That SpongeBob needs to keep his pet out of my yard. I am sick of cleaning up after him.

Gary: Meow. [Squidward discovers Gary leaving trail all over his pet rock collection]

Squidward: Not my pet rock collection. [growls, turns red in anger and starts jumping up and down angrily] That's it! This isn't the first time you've soiled my yard with your revolting excretions. But mark this down in your little notebook: it will be the last time!

[Bubble transition to Squidward furiously putting up a force field of wood all around his house. Suddenly, he winces in pain from a wood splinter he sustained.]

Squidward: This cheap, splintering wood will keep even Gary out.

[Bubble transition to Squidward relaxing outside with wood fencing surrounding him.]

Squidward: Now, I feel safe. [Gary's trail drops all over him] SpongeBob!

SpongeBob: Hi, Squidward.

Squidward: [calmly] Hey, SpongeBob... [screaming furiously] Keep your shelled vermin off of my property! The next time, my annoyingly yellow neighbor, your wet pet oozes on my lawn, you leave me no choice but to call Snail Control. That little monster... [Gary angrily bites Squidward's butt, causing him to stutter.] He bit me!

SpongeBob: [pulling Gary away chewing on a piece of Squidward's shorts] Gary! No, dirty boy. This isn't like you.

Squidward: Oh, but it's just like you, SpongeBob, to raise such a misbehaved mollusk.

SpongeBob: Gary's not misbehaved! [Gary growls viciously.] But there does appear to be something wrong with him.

Squidward: [Patrick arrives.] I'll say. I hope he had his shots.

SpongeBob: Oh, of course.

Squidward: All of his shots?

SpongeBob: [giving a thumbs up] Affirmatory.

Squidward: For rabies?

SpongeBob: Yup.

Squidward: Snail pox and soft shell dance?

SpongeBob: Yupie.

Squidward: Bronchitis, lumpy-bump trump, teen angst?

SpongeBob: Yup, yup, yup.

Patrick: [suddenly appearing] Well, let's not forget the worst of them all: Mad Snail Disease.

SpongeBob: Uhh...

Patrick: You mean your pet hasn't been vaccinated for mad snail disease? [to Squidward] Looks like the rash has already started.

Squidward: Rash?

Patrick: Tell me, do you have any soreness of throat?

Squidward: [gulps] Uhhh, well, now that you mention it, my throat is a little dry.

Patrick: This disease will ravage your body with bloodshot eyes, loss of balance, messy pants, ticklish rib cage, severely untrimmed toenails, and finally, the bite from that infected snail will turn you into...a zombie.

[Squidward freaks out; screams, then runs off crying loudly.]

Patrick: [to SpongeBob] You need to get that snail of yours to a doctor before he bites someone important. [both gasp once they see that Gary is missing] There's a mad snail on the loose! [runs off screaming]

SpongeBob: Gary? [zoom out to his and Squidward's homes] Gary?! [zoom out to Earth] Gary?! [zoom out to the Milky Way] Gary?!

Patrick: [runs up to a couple] The mad snail is coming! If he bites you, you'll turn into a zombie.

Fish: Jeepers, what's with all the lunatics? [Gary crawls up]

Fish's Wife: Oh look, honey, isn't he the cutest? [Gary is panting]

Fish: Come here, little buddy. [pets Gary] He's just adorable. [Gary angrily bites him] Mad snail disease is real! I'm a zombie. I've been bitten by a mad snail. I've got mad snail disease!

Fish #2: Then I've got it! A snail just bit me, too! [all screaming]

[Incidental 42 screams; all look at their hands and scream. Cut to a "Please Stand By" screen.]

Realistic Fish Head: We interrupt this broadcast to bring you a [screen now shows "News Blast"] news blast. [reading the news headline on the screen] Terror in a shell. [snail mouth transition, then zoom out to Johnny Elaine on the anchor desk] This just in... fear and disease are spreading like wildfire [cut to an outline of Gary] as a killer snail has been biting the denizens of Bikini Bottom infecting them with... mad snail disease. [two scream sound effects are played at once. One of them is from "Hooky," and the other one was used on the show Rocko's Modern Life] Ask any old fish on the street and they'll tell you that [cut to an outline of Squidward] germs enter through the bite radius, traveling upstream until the entire host body is full of... mad snail disease. [the same sound effect from above can be heard] We now take you to Action News Reporter Perch Perkins live on the scene.

Perch Perkins: Perch Perkins here with the first victim of this epidemic. Tell me, Mr. Tentacles, when did you first begin to suspect you were a zombie?

Squidward: Well, after I was bitten by a mad snail, I began to get a rash followed by loss of balance, ticklish rib cage, and a few other symptoms.

Incidental 105: [runs up to them] Hey, I was bitten by a snail. I kinda feel off balance. [falls over] Whoa.

Perch Perkins: Hey, I have ticklish ribs too, and I haven't even been bitten.

Incidental 105: Oh no, it's spreading through the air! [all scream]

Perch Perkins: Well, you heard it here first. We're all doomed to a horrible demise. Thanks to a diseased snail. [screams and runs around in circles; TV static then back on; still screaming as the camera zooms out of a television store. Everyone but SpongeBob screams and runs away.]

SpongeBob: [shocked due to the news] Gary? [horn honking] I can't believe that sweet and slimy snail would cause all this destruction.

Squidward: [moaning] I'm a zombie... here to dine on your squishy yellow flesh! [moaning like a zombie. Some of the people moan and are zombies, closing in on SpongeBob, who then screams and takes a bus. As he hops off the bus, the zombies follow SpongeBob again. He still screams while running to the Krusty Krab.] It's locked! [all moaning] Somebody let me in.

Mr. Krabs: SpongeBob, come in, boy. And bring your friends in, too. They look hungry. [uses key to open]

Incidental 42: Stop! You can't let anyone in!

Mr. Krabs: But they just want to dine on some Krabby Patties.

Incidental 42: They're zombies. They only want to dine on our flesh.

Mr. Krabs: Arrgh, alright, but it's coming out of your paycheck.

Incidental 42: I don't work here.

SpongeBob: But, Mr. Krabs, it's me, SpongeBob.

Mr. Krabs: But how do we know you haven't become one of those voracious flesh-eaters?

SpongeBob: Could a voracious flesh-eater do this? [he uses his body to slide through the door]

Mr. Krabs: SpongeBob, it's you.

SpongeBob: That's right. So let me in before I'm eaten.

Mr. Krabs: Yeah, that's SpongeBob all right.

Patrick: Or is it?

SpongeBob: Huh?

Patrick: I don't believe that's the real SpongeBob. He looks pretty zombified. Just look at how yellow he is.

SpongeBob: Come on, Patrick, would a zombie have a picture of his best buddy in his wallet? [shows a Best Buddies 4-Life picture]

Patrick: Perhaps not, but I got my eye on you!

Old Man Walker: If you could pull out your eye and put it on him, wouldn't that make... you a zombie too? [everyone gasps]

Patrick: You're right. [alarmed] I'm a zombie!

Old Man Walker: Who's to say we're not all zombies?! [all scream and run wildly]

Gary: Meow. [everyone gasps as he slithers out of the kitchen]

All: The snail!

SpongeBob: Gary! Are you okay, buddy? Come here, boy.

Incidental 40: No, don't get near it. Oh, the pity of it all!

Incidental 14: [to Harold] I can't watch. [faints into Harold's arms]

SpongeBob: All those people think you're a monster. But I know you're just a snail. [pets Gary]

Gary: Meow, meow, meow! [angrily bites SpongeBob's arm, causing everyone to gasp]

SpongeBob: [looks at his bitten arm] Gary... [sniffling] How could you?

Gary: [ferociously] Meow, meow, meow!

Incidental 40: SpongeBob's been infected by his own pet snail. Oh, the irony! Quick, we must quarantine that infected snail before he bites every last Bikini Bottomite. Let's get the snail!

All: Yeah! [SpongeBob gasps as they hoist jellyfish nets and torches.]

SpongeBob: No! Don't hurt him!

Incidental 40: Hand over the snail!

Mr. Krabs: It's... for his own good, SpongeBob.

SpongeBob: No! I won't let you touch Gary!

Incidental 40: [grabs SpongeBob] Stop the madness, man! The Mad Snail Disease ends now! Seize the snail!

Doctor Gill Gilliam: Halt! Did someone say 'Mad Snail Disease'? Is that what all this fuss is about?

Patrick: Yeah. What do you know about it?

Doctor Gill Gilliam: Funny you should ask. Allow me to introduce myself. Doctor Gill Gilliam. S.D.E. and S.E.

SpongeBob: S.D.E. and S.E.?

Doctor Gill Gilliam: Snail disease expert and snail expert. I'm sorry to break this to you all, but that 'mad snail disease' you're talking about, it doesn't exist.

All: Huh?

Doctor Gill Gilliam: That's right. No such thing. It's an old urban legend. A myth.

Patrick: Well, does that mean we're not zombies?

Doctor Gill Gilliam: Of course not. No one is. It's just mass hysteria.

Incidental 60: But what about my severely untrimmed...

Doctor Gill Gilliam: Those are only moderately untrimmed. All the supposed symptoms are just common ailments.

SpongeBob: [holding Gary back] Easy, boy. But what about Gary then? If he doesn't have a disease, why'd he bite all those people, including me?

Doctor Gill Gilliam: Hmmm... mm-hmm-mm. [notices a wooden splinter] Ahh-ahh! The problem's right here. He's got a little splinter in his foot. [The doctor pulls out the splinter and Gary is now back to normal, a zoom out shows that the splinter was one of Squidward's logs, just as an example] I'm sure this was causing him to stamper, making for serious grouchy snailitis.

SpongeBob: Oh, Gary, I knew you weren't disease-ridden. You still love me?

Gary: Meow.

SpongeBob: [laughs] Good ol' Gary's back. [Sandals, Bill, Nathaniel, Charlie, and VB get mad when Squidward comes in and keeps acting like a zombie] Hey, Squidward? You're not a zombie, remember?

Squidward: Oh, yes I am. [puts on his work hat as Nathaniel walks up to order] Welcome to the Krusty Krab. May I take your order?

Mr. Krabs: All's well that ends well.

[Gary angrily bites Mr. Krabs' butt]

Mr. Krabs: Ow! [tries to kill the pain, then looks at Gary as the episode ends]