The Secret Box / Band Geeks - S2-E14
Revealing mistake: When Squidward asks who has played instruments before and Plankton responds, look at Plankton's triangle. The bottom disappears for a split-second.
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.
Revealing mistake: When Spongebob and Mr. Krabs are rolling in the pile of money, dollar bills are flying into the air. After crossing an invisible line, the dollar bills disappear in mid-air. (00:11:35)
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)
Mermaid Man and Barnacle Boy III / Squirrel Jokes - S2-E4
Revealing mistake: When we see Billy get told about the stupid squirrel, he has a sleeve going through his arm. The moment he starts talking, the sleeve disappears and his arm extends over his shirt. Around the end of the shot when he's being pulled away, the sleeve returns.
Big Pink Loser / Bubble Buddy - S2-E3
Revealing mistake: Big Pink Loser: When Patrick is answering phone calls, the third time he picks up and says, "No, this is Patrick", the anchor symbol on his hat briefly vanishes. (00:04:36)






Answer: Because it's a Spongebob cartoon. Nothing makes logical sense.
Brian Katcher