Krab Borg / Rock-a-Bye Bivalve - S3-E8
Revealing mistake: In the shot that shows the outside of the Krusty Krab (in Krab Borg) they reused the drawing of right before the customers ran out of the building because you can see many customers crowded at the door. This shot lasts about 2 seconds but it's not hard to spot. (00:08:05)
Krab Borg / Rock-a-Bye Bivalve - S3-E8
Continuity mistake: In the scene where SpongeBob has given his pants to the clam, two continuity errors appear. First, Patrick puts his head in the pants and he says that the clam is hungry. A lot of holes are in his head. In the very next shot, the holes are gone. This is really obvious. The other continuity error is that before Patrick gets those holes, SpongeBob isn't with his pants. When he tries to give the Patty to the clam, he's suddenly with his pants, when the little clam is supposed to have his pants.
Krab Borg / Rock-a-Bye Bivalve - S3-E8
Continuity mistake: In "Rock-a-Bye Bivalve," near the end, the timecard says it's midnight and it is dark outside. However, when the bivalve flies away, it's morning (judged by the shadows of the houses, even late morning), even though just a few minutes passed.
Krab Borg / Rock-a-Bye Bivalve - S3-E8
Continuity mistake: In Rock-a-Bye Bivalve, Spongebob's tie turns black when he is doing the chores on Patrick's second day of work, and then turns back to normal when he walks into the living room.
Krab Borg / Rock-a-Bye Bivalve - S3-E8
Continuity mistake: In "Rock-a-Bye Bivalve" when Spongebob and Patrick hear the bivalve chirping, the coral that vibrates is bright green and is standing up straight. However, when they find the bivalve and take it out from behind the coral, the coral is dark green and is bent over.
Krab Borg / Rock-a-Bye Bivalve - S3-E8
Continuity mistake: Rock-a-Bye Bivalve: When Patrick gets home from the party after midnight SpongeBob is angry, and as Patrick walks out in the interior shot the front door is wide open on the inside of the home, but in the next exterior shot the front door is wide open on the outside of the pineapple.
Krab Borg / Rock-a-Bye Bivalve - S3-E8
Continuity mistake: Krab Borg: The door to Krabs' office has a porthole in many shots, but after Krabs burns his eyes he rushes out of his office into the eating area, and when he runs past Squidward and SpongeBob the office door is the normal solid door, with an anchor on the exterior side.
Krab Borg / Rock-a-Bye Bivalve - S3-E8
Continuity mistake: In 'Rock-a-Bye Bivalve' Spongebob's front door changes hinge sides. Also at the end suddenly there's a light switch next to the door which wasn't there earlier.
Krab Borg / Rock-a-Bye Bivalve - S3-E8
Continuity mistake: The scene in episode Rock-a-Bye Bivalve where SpongeBob and Patrick start arguing about working for Junior at Patrick's house, SpongeBob is not inside the house. While SpongeBob is staring down at Patrick, his head is sticking out of the top of the hole in the ground. Once SpongeBob jumps in the top of the hole is way past their head.
Answer: I believe this is the Season 6 episode "Spongicus".