Continuity mistake: Gary leaves big saliva trails. When Squidward realizes that Gary leaves these saliva trails, we can see that is a trail in front of Squidward's house. When Squidward tells SpongeBob about these trails in the language of the past, we can see that the trail of the saliva has changed: it bigger and almost in all the scenery. After a while, we see that the road goes directly to Squidward's house, to its door. How did the road change, if we haven't seen Gary moving?
Continuity mistake: When Spongebob shows Patrick the good noodles chart all the stars are wildly scattered in each row. When Patrick is trying to announce his name to the class they're all in a neat row. When Mrs. Puff is removing the star from Spongebob's row they're scattered again.
Continuity mistake: In "Squid's Day Off" Squidward gets mad at Spongebob for ringing a bell over and over again. It shows the bell in the window to the left. Later, when it shows Squidward throwing the cash register onto the ordering desk, the bell is gone from the window. In the next shot of Spongebob, the bell is back in the window. Then, when Squidward shouts "No." the bell is gone again.
Continuity mistake: When Spongebob is outside, and he takes out his "to do list" at first he is holding it with his right hand, but when it shows the front of the paper, you see that it is his left hand. Then it is his right hand again.
Revealing mistake: In "Spongebob Meets The Strangler" when that fish holds up Spongebob's dry cleaning at the supermarket, it looks like he is holding it up with a coathanger because his hand is up in the air, but you can easily see nothing is holding it up. It's just floating up in the air.