The Thing/Hocus Pocus - S4-E16
Continuity mistake: The Thing: When Squidward is riding his bike on the road, he hits a cement truck, and gets covered in cement. He tries to get out of it, and a shot later, the location suddenly changes from the road to a green hill.
Best Day Ever/The Gift of Gum - S4-E20
Revealing mistake: When Squidward says "I suppose if you haven't fixed my clarinet, the concert would have been a bust", Sandy's tail is the same color as her suit.
Have You Seen This Snail? - S4-E3
Continuity mistake: In "Where's Gary?" the length of the paddle ball string that SpongeBob uses seems to vary in certain shots. While the length is somewhat subjective one shot that is more conclusive is when Patrick finds Spongebob lying on the floor. The string on the paddle ball is fairly short. When the two get up to get a glass of milk, the string is now a lot longer.
Selling Out/Funny Pants - S4-E5
Continuity mistake: In "Selling Out", at the end, all the customers leave the Krusty Krab. But when the Krusty Krab floods, the place is packed with customers.
Plot hole: In "Once Bitten", Mr. Krabs never unlocks the doors to the Krusty Krab, but at the end of the episode, Squidward enters with no problem.
Suggested correction: Maybe Squidward has a key to the Krusty Krab that Mr. Krabs doesn't know about.
He could still have a key, but we don't see it.
Whether or not Squidward owns a key to the Krusty Krab is beyond the point of the mistake here. The point is that Squidward is able to walk into the Krusty Krab despite the doors being locked, and he doesn't use a key or anything else to unlock them. He just pushes them open.
Maybe the doors were not locked properly.
Skill Crane/Good Neighbors - S4-E4
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.
Enemy In-Law/Mermaidman and Barnacleboy VI: The Motion Picture - S4-E7
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.
Enemy In-Law/Mermaidman and Barnacleboy VI: The Motion Picture - S4-E7
Other mistake: Plankton's phone doesn't have a 0 button on it.
Fear of a Krabby Patty/Shell of a Man - S4-E1
Continuity mistake: In the episode 'Shell of a Man", when SpongeBob pushes over Mr. Krabs' shell off of the chair at Mr. Krabs' desk, you can see that there are 2 eye holes, a nose hole, and a very large hole for the mouth. But when SpongeBob puts the shell on, both his nose and mouth are in the large mouth hole, and his eyes are in the eye holes. But there is no nose hole.
The Thing/Hocus Pocus - S4-E16
Continuity mistake: At the start of "The Thing" the walkway to Patrick's house is missing.
Best Day Ever/The Gift of Gum - S4-E20
Character mistake: SpongeBob tries to steal the gum off his door at night. The next day, SpongeBob says that it was still Best Friends Day, so he would give Patrick his gum back. Really, it should have been the next day.
Patrick SmartPants/SquidBob TentaclePants - S4-E8
Plot hole: In 'Patrick SmartPants' Patrick lost the top of his head after falling off a cliff, but Spongebob put it back on. Suddenly Patrick's intelligence skyrocketed, but wanted to return to his former self in the end of the episode. To do this he re-enacted his fall, but it was unsuccessful. They eventually figured out that Spongebob had in fact not put on Patrick's head, but a 'brain collar'. How did Patrick posses his memories throughout the 'intelligent phase' despite not having his own head (and brain)?
Continuity mistake: In "Once Bitten", Mr. Krabs is holding a key, about to unlock the doors to the Krusty Krab, when a customer stops him. Two shots later, the key is missing from his hands.
Krusty Towers/Mrs. Puff, You're Fired - S4-E9
Continuity mistake: When the rocks fall out of Patrick's suitcase, the rocks change number and position between the 3 shots.
Skill Crane/Good Neighbors - S4-E4
Continuity mistake: During "Good Neighbors" Squidward is sitting on his couch trying to enjoy his afternoon. SpongeBob and Patrick pop up behind him. In the next shot. Instead of Squidward sitting on his couch with Bob and Pat behind him, they are standing in the middle of the kitchen.
Born to Be Wild/Best Frenemies - S4-E18
Continuity mistake: When we first see Plankton, the distance between him and the Kelpshake store keeps changing between shots. (00:02:20)
Patrick SmartPants/SquidBob TentaclePants - S4-E8
Continuity mistake: When SpongeBob and Squidward are combined, Squidward's arm is on the left and SpongeBob's arm is on the right, and that's how it is the whole time. Except in one shot, the shot of SpongeBob's head after Squidward says, "yellow freak." Look at the bottom and you'll see two SpongeBob arms, when the one on the left is supposed to be Squidward's.
Bummer Vacation/Wigstruck - S4-E14
Continuity mistake: In Wig Struck, Patrick takes a bite out of Spongebob's wig and in the next shot, the wig is restored.
Bummer Vacation/Wigstruck - S4-E14
Deliberate mistake: When SpongeBob is playing with his Krusty Krab action figures, their faces change expressions instantly.
Have You Seen This Snail? - S4-E3
Revealing mistake: After SpongeBob tells Patrick, "I can't find Gary," text that reads "Rough Draft Korea" briefly appears on screen during the bubble transition. (00:08:24)
