The episode starts out when two customers park at the Chum Bucket. Plankton thinks they want to eat there, but they were parked there because they couldn't find parking at the Krusty Krab. Karen then suggests that Plankton should advertise his product. Plankton then hangs a sign that says "CHUM IS METABOLIC FUEL!" Patrick comes along and tries to read the sign, but his head starts smoking from the strain of trying to understand what these new words are. After his head is put out, Patrick then rearranges the letters, so the sign reads "CHUM IS FUM!" The new slogan starts to attract customers. Plankton hires Patrick as his slogan manager.
Meanwhile, back at the Krusty Krab, Mr. Krabs believes Plankton has stolen the secret formula, so he comes up with a plan to steal the formula back. Plankton sees through SpongeBob and Mr. Krabs' disguise and they realize that it was the slogan that brought in the customers, despite the fact the chum tastes awful. To combat the disgusting taste of the chum, the customers simply say "Chum is Fum" over and over. Then Plankton goes to Patrick to check on how his assignment to come up with new slogan ideas is going. However, all Patrick does is write Chum is Fum in a thousand different ways. Plankton then gets mad at Patrick, but cools down because Patrick's slogan is still attracting customers.
A few days later, people are getting bored of the slogan, so Plankton and Patrick hold a board meeting. Patrick comes up with a new slogan three days later, changing it to "FUM IS CHUM!" This brings back Plankton's customers, much to the chagrin of Mr. Krabs. Business is so large that Plankton gets into the restaurant magazines and even a Canadian hockey team shows up to eat. Patrick then decides to resign from his position as advertising director because he is "burnt out" - there is literally a hole burned into the back of his head. Plankton protests, but then bluffs to make Patrick believe that he is disposable, and not necessarily to keep customers eating at the Chum Bucket. During his rant, Plankton accidentally insults his customers over the intercom that he had installed by the cash register earlier to taunt Mr. Krabs. His customers hear him calling them "buffoons, morons, the dumbest of the dumb" among other things, which causes all his customers to abandon their chum in anger. Plankton then gets beaten up by the hockey team. At the end, everyone sees Patrick finishing a sign with the Krusty Krab's new slogan, "KRABBY PATTIES ARE FUM!" and everyone returns to the Krusty Krab.
Plankton claims he has never met Patrick but in other episodes, before this one, he has met him and worked for him. It is possible Plankton could've forgotten that Patrick worked for him since they may have not encountered each other in a while or that this episode chronologically took place earlier in the series.
There is an online game based on this episode called, Chum is Fum. In the game, the player makes the customers eat the Chum Sticks.
When the hockey players first heard Plankton talking about his customers in a bad way, there were five of them. However, when they were about to attack Plankton with their hockey sticks, there were only four of them.
When Patrick was first seen putting up the sign for the Krusty Krab, the hole in the back of his head wasn't seen. When Patrick was seen for the last time, the hole is now on at the back of his head.
When Plankton was stomping on the ripped paper in anger, his head was still messed up. However, in the next shot when Plankton was yelling on how he's tired of the Krusty Krab stealing his customers, his head was suddenly fixed.
At the end of the episode, when Patrick finishes the point in the exclamation mark in "KRABBY PATTIES ARE FUM!" the ladder he is stepping on is shorter and he is below the sign, but in the next scene, automatically the ladder is longer and he is next to the sign.
When Plankton was going through the Box of Letters, the front door to the Chum Bucket was missing.
The path to the Chum Bucket seems longer than usual in this episode.
At the end of the episode, when SpongeBob and Mr. Krabs were in the front of the Krusty Krab, the Chum Bucket could not be seen.
When Mr. Krabs says "A few hours ago, the Chum Bucket was, as it should be, a desolate no-man's land," "bucket" is muted. This only happens on TV airings; all other releases of this episode have this error fixed.