Bubblestand / Ripped Pants - S1-E1
Revealing mistake: In "Ripped Pants", Spongebob plays the guitar and chord changes are heard, but his fingers on the neck of the guitar do not move.
Help Wanted / Reef Blowers / Tea at the Treedome - S1-E2
Revealing mistake: When Spongebob uses his binoculars, his teeth turn yellow for one frame.
Help Wanted / Reef Blowers / Tea at the Treedome - S1-E2
Revealing mistake: In the shot where Spongebob says, "That little squirrel is in trouble, " half of his belt is missing.
Culture Shock / F.U.N. - S1-E10
Revealing mistake: In "Culture Shock" when Spongebob takes the green fish's order, he has a pencil tucked in his ear, but he doesn't have an ear, so it's just floating in thin air. (00:01:55)
Revealing mistake: After SpongeBob disguises himself as Patrick's rock and right before he sneezes his uvula clips through his bottom lip.
Revealing mistake: At the beginning of Rock Bottom, when the bus pulls up in front of Patrick and SpongeBob, right before Patrick steps up onto the bus, SpongeBob's right arm is missing and it suddenly appears as he starts moving.
Revealing mistake: Near the end of "Rock Bottom", when SpongeBob arrives back to Bikini Bottom, SpongeBob's pineapple is animated differently from the other buildings. It looks like it was cheaply tacked on in post production.
Answer: I believe this is the Season 6 episode "Spongicus".