- SpongeBob SquarePants
- Patrick Star
- Squidward Tentacles
- Realistic Fish Head
- Plankton (speaking cameo)
- Mr. Krabs (cameo)
- Mrs. Puff (cameo)
- Fred Rechid (brief cameo)
- Gary the Snail (cameo)
- Citizens of Bikini Bottom
As an iceberg travels across to the surface of the water above Bikini Bottom, causing it to snow underwater. Everyone is having fun in the snow, and SpongeBob and Patrick decide to have a snowball fight. Meanwhile, Squidward is relaxing at home with a cup of tea. He hears the sounds of SpongeBob and Patrick's fighting and tells them to quiet down. They try to convince him to come out and play with them, both trying to get him on their own side.
Squidward decides that, as entertainment, he will watch them fight, hoping they will get hurt. SpongeBob and Patrick realize that snowball fights are for children, and they sign a peace treaty. Squidward tries to convince them to continue, but gets hit with a snowball. He then decides to join in the fight. He makes a small fort which provides him no protection, and soon begins making it larger. He begins relentlessly pelting SpongeBob and Patrick with snowballs, and hits everyone with snowballs, and soon his fort has grown into a tower.
After being hit by a snowball containing his clarinet, SpongeBob and Patrick decide that Squidward is taking it far too seriously, and go back inside. A paranoid and riled-up Squidward does not realize that the fight is over, and continues to throw snowballs, as an overhead palm branch keeps dropping snow on his head. Meanwhile, SpongeBob and Patrick relax in the pineapple watching TV with hot chocolate and popcorn.
- "The Snowball Effect"" is also the title of a famous short story by Katherine MacLean.
- While it was Bikini Bottom's first actual snow day, this really marks SpongeBob and Patrick's second winter-based fun since "Survival of the Idiots".
- This episode marks the fourth appearance of snow, the first three being "Bubble Buddy", "Christmas Who?" and "Survival of the Idiots", and later in "Frozen Face-Off".
- Running Gag - Squidward's fireplace is put out by a stray snowball.
- When Squidward is sitting next to his fireplace, a replica of his head with moose antlers is seen hanging on a plaque on a wall.
- This is the first time SpongeBob turns into a rapid fire weapon.
- A tiny clip of this episode was shown in a Lego SpongeBob commercial.
- Netflix mistaked the title for, "The Snowball Effect".
- When Mrs. Puff blows the snow off her boat and onto a nearby fish, the fish pops his head out, and yells "Hey!", although his mouth doesn't move.
- When Squidward is demonstrating his fort and how it should be used, and Patrick throws snowballs at him, his arm doesn't move.
- When SpongeBob is first seen with his fort, it is circular and shorter than him. But when the camera returns to SpongeBob, his fort has changed shape and is about as tall as him. And when the camera returns to SpongeBob again, his fort returns to how it originally was.
- When Squidward drops his snowball after he refuses to be on neither Patrick or SpongeBob's side, the mark that he makes in the snow disappears when the camera pans out.
- When the camera shows Patrick laughing after hitting SpongeBob with a snowball, his fort is smooth. Before, it was full of bumps. Also, when Patrick comes upon the barrage of snowballs SpongeBob serves at him, his fort is bumpy again. Also, all the square snowballs he was seen with are gone.
- When a closeup of the DNA strand snowball Patrick made is shown, the sky is light blue instead of gray.
- When Patrick tries to make a snow angel, he only makes a circle.This might be a reason because he's a sea star, and he already is a snow angel shape.
- In the beginning during the news report,when the sign changes from stop to go,the snow that was on it before it changed levitates.