Continuity mistake: When Spongebob has melted from stress and exhaustion, he is trying to talk and Sandy tells him to "hold that thought", and you can see the bike that they were riding, in the background. When she makes the fly fishing joke, the bike is gone, and there is a small plane. A few shots later the plane is gone as well.
Continuity mistake: When Spongebob is outside, and he takes out his "to do list" at first he is holding it with his right hand, but when it shows the front of the paper, you see that it is his left hand. Then it is his right hand again.
Continuity mistake: When Pearl gives SpongeBob the new costume for the Krusty Krab, she gives SpongeBob a mirror. In the mirror, Squidward appears and tells him not to accept the costume. If you notice, Squidward is at the LEFT of SpongeBob. Because is a mirror, in the real life he would be at the RIGHT of SpongeBob. When a shot is shown of SpongeBob and Squidward, you can see that Squidward isn't at the RIGHT of SpongeBob, he's at the LEFT.
Continuity mistake: In the episode "The Bully," when Flats punches Spongebob, Spongebob states to Gary that he's made out of some spongy material, that it absorbs his blows and it doesn't hurt him at all. But in later episodes, when Spongebob gets knocked out that never happens anymore.
Character mistake: In the beginning of "One Krabs Trash" Spongebob only has one bill in his hand, a 5 dollar bill. When he goes to his house and comes back, he says he found 68 cents. Therefore, he has 5 dollars and 68 cents. However, he has two dollar bills and a few pennies in his hand, which cannot be made into $5.68.