Eek, an Urchin!

Characters

This is the third time the Krusty Krab thermostat is used. The first was in Krabs a la Mode and the second time was in Planet of the Jellyfish.
In comparsion, the sea urchin in this episode is about the same size as Plankton.
This is the third time Plankton actually teams up with Mr. Krabs in order to solve a problem. The first was in Best Frenemies and the second was in The Other Patty.
This is the second time Mr. Krabs' money was eaten, in this episode's case, by the urchin. The first was by Mystery back in the episode My Pretty Seahorse.
The title card for this episode looks similar to the title card for Demolition Doofus.
Running Gag: Someone using a telephone or cell phone.

When Plankton first entered the Krusty Krab and saw SpongeBob, Mr. Krabs, and Squidward together, they were all in front of the register and closer to the front door. When Plankton jump onto SpongeBob's face after seeing the urchin, they were all suddenly beside the register and closer to the kitchen.
When Plankton's robot first entered the Krusty Krab through the front door, the Chum Bucket couldn't be seen.
After Mr. Krabs destroyed Plankton's robot with the mallet, he throw it away. When he saw the urchin in his register eating his money, he suddenly had the mallet again.
When Mr. Krabs was boarding up the door to the kitchen, the thermostat wasn't seen. When Squidward appeared again, the thermostat was there.
Also, after Squidward turned down the themostat way down and Mr. Krabs and SpongeBob went into the kitchen, the door wasn't boarded anymore.
When Mr. Krabs is turning the thermostat back up, a table (which Plankton was sitting on) is suddenly there.
Once Frankie Billy squirted ketchup on the sea urchin, when they showed the next scene of him, the ketchup vanished.