Continuity mistake: In "Bubblestand" after Squidward blows the huge bubble, he tells Spongebob and Patrick that the ability to blow bubbles is in his genes. If you look at the position of the bubblestand sign, the sign is facing the direction Squidward is talking. The sign had always been facing the street, which means that Squidward was actually talking towards the street, when Spongebob and Patrick are actually to his right.
Add timeMr. Freeze
Continuity mistake: On "One Krab's Trash", when Mr. Krabs draws a ghost on a sheet of paper, it shows before it goes into Spongebob's rooms that there's only writing on one side (i.e. the ghost) and when it goes into his room, a shopping list is on the back.
Continuity mistake: When Spongebob first shows the Patrick the technique for bubble-blowing, there are two red corals in the background - one on his right and one on his left. Later, when he shows Squidward the technique the red coral on the left side of the screen disappears.
Add timeMr. Freeze
Continuity mistake: In "No Weenies Allowed", the gatekeeper in front of the sailor club has a tattoo on his front with a heart and MOM on it. Sandy rips it out and places it back upside down. It now shows an upside down heart with WOW. In the next cuts between this and when Spongebob gets sent to the Weenie place, the tattoo suddenly has the heart downside up reading WOW, or upside down reading MOM. This is never possible because MOM was supposed to be with the downside up heart, not the upside down heart.
Continuity mistake: During "Good Neighbors" SpongeBob is in Squidward's house talking to him while he is in a pink nightgown. Squidward throws SpongeBob out of his house while he is in his regular brown shirt. When he is back in his house, he is in his pink nightgown again.
Continuity mistake: Patrick turned out to have put the lens cap on the camera before they started to film. But when the first scene was being filmed, there was no sign of the lens cap on the camera. There was also no sign of the lens cap on the camera when the Pearl "Boatmobile" fell off the cliff.
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Other mistake: In the episode "Sandy's Rocket", Spongebob and Patrick go "alien-hunting." SpongeBob and Patrick are in Squidward's house. But when SpongeBob holds the hot water bottle, and he says "No, it's an egg-sack!", one of the drops leaking from the bottle goes up instead of down.