Help Wanted / Reef Blowers / Tea at the Treedome - S1-E2
Trivia: In the episode "Help Wanted", Spongebob has a pet flying scallop in a cage hanging from the ceiling in his room. It is never seen again in the entire series.
Suggested correction: Very wrong. SpongeBob's pet scallop, Shelley, can be seen in SpongeBob's room in many episodes throughout the show. Some examples shortly after this episode include "Home Sweet Pineapple," "Opposite Day," and "Suds." You can find all of Shelley's appearances here: https://spongebob.fandom.com/wiki/Shelley/appearances.

The Sponge Who Could Fly (aka The Lost Episode) - S3-E16
Trivia: The miner who gives Patchy the video tape is Stephen Hillenburg, the creator of SpongeBob SquarePants. (00:04:53)
The Nitwitting/The Ballad of Filthy Muck - S12-E2
Trivia: In "The Ballad of Filthy Muck", there's a citizen that reads the newspaper headline that has an overly-large nose. His speech pattern and caricature nose is impersonating Jimmy Durante.
Spy Buddies / Boat Smarts / Good Ol' Whatshisname - S5-E4
Trivia: At the end of "Spy Buddies", Plankton gives Mr. Krabs $1, as part of the usual bet. This is a reference to "Trading Places", where the Duke brothers' usual wager was $1.
The Bully / Just One Bite - S2-E17
Trivia: In "Just One Bite", there was a deleted scene where Squidward enters the Krusty Krab at night. Squidward opens the door, and a bucket of gasoline falls and spills all over the ground. A robotic arm drops a lit match to light the gasoline.
Trivia: For an unknown reason, the opening credits of both episodes are a lighter blue than usual.