Continuity: In the episode Jellyfishing, Squidward was holding the net in his left hand. When he was catching a jellyfish, the net was in his right hand. When he was chased by a huge jellyfish, the net was back in his left hand.
Revealing mistakes: In the episode where Spongebob is making his own Mermaidman movie, it is said that Patrick kept the lens cap on during the entire film, but, you can easily see that that is not true, since you see the camera filming without a lens cap.
Continuity: In the episode where Patrick goes to Boating School with SpongeBob, Spongebob writes Patrick's name on the board in all caps. Later on, it is seen in the background with only the 'P' capitalized.
Errors in geography: The geography in Spongebob's house and Bikini Bottom changes almost every episode.
Continuity: When Plankton is turning the thermometer in the Krusty Krab, you can see he is turning the knob back and forth. Yet you see the temperature is just going down, not up and down like it should be.
Revealing mistakes: At numerous points in the series, the phrase "Galley Grub" on the Krusty Krab menu is misspelled as "Gally Grub."
Errors in geography: Spongebob's house in relation to the Krusty Krab's location varies throughout the series.