Continuity mistake: When Spongebob comes home after being arrested, he picks a spare key up from under his mat and gets angry at himself for trying to break in the night before. When he walks in, discomfort on his face, the mat is gone.
Continuity mistake: In "Jellyfish jam", when SpongeBob shows the jellyfish to Squidward, and the jellyfish starts to do a lot of things, you see that Squidward is looking by his porthole in his house. The porthole is closed. However, when he says "How can anybody have fun with a jellyfish?" his arms go outside the porthole. But this is impossible, since the porthole is closed.
Continuity mistake: In Squirrel Jokes, when Spongebob comes out for his second act, there's a back shot of a crowd, and there is one guy in the front right (from the back view) who is green. There is another front shot of the crowd and the guy completely disappears.
Continuity mistake: When Squidward has sort of a strict conversation with Spongebob, Mr. Krabs, and later Patrick, the 3 of them he was talking to, were side by side, but a shot later, Mr. Krabs and Spongebob are side by side, but farther from Patrick.