They are fish hooks used by fishermen and contain plastic fish attached to them that vary in appearance. The ones at Fish Hooks Park are covered with cubed cheese.
Role in series
At the Krusty Krab, Mr. Krabs warns everyone that the hooks have returned to Bikini Bottom. He explains that the fishermen are using them to reel sea creatures out of the ocean and into land, followed by selling them at a gift shop or trapping them inside a tuna can, which contains the smell mayo, to eat them. After finishing his speech, he strongly urges everyone to stay away from them.
Upon returning to the kitchen, Patrick pops his head into a window and tells SpongeBob that the carnival has come to town and suggests that he take a break from work to join in on the fun. Although reluctant at first, the latter adheres to this and follows him to the "carnival," which then turns out to be Fish Hooks Park. Upon witnessing this, SpongeBob is worried about his best friend's well-being.
Patrick sees no harm, and indulges in the free cheese attached to the hooks, much to SpongeBob's horror. SpongeBob then tells him that Mr. Krabs warned him about the hooks, though Patrick encourages him by saying that Krabs didn't say he couldn't "ride on them like a horsey." Conforming to peer pressure, SpongeBob eventually joins Patrick in playing on the hooks and the pair then proceeds to jump off after reaching their destined height, to the fishermen's disappointment.
Playing on the hooks with Patrick has caused SpongeBob to miss his a majority of his job. As a result, Squidward takes his place in the kitchen for the time being, while Mr. Krabs checks to see where SpongeBob is. Amongst witnessing him and Patrick playing on the hooks, Krabs warns them about doing so and strictly recommends that they never do it again, to which they promise.
The following day, Patrick breaks his promise and plans on playing in Fish Hooks Park again, encouraging SpongeBob to skip work and do the same. However, the latter refuses and keeps his promise. Upon walking to work, SpongeBob encounters a hook in the middle of the street and tries to resist, but eventually gives up and plays on them once again.
The hook manages to be unremovable from his pants. Attempting to hide it, SpongeBob confronts Mr. Krabs about the hook and eventually admits that he was playing on them despite several warnings not to. As a result, the only solution to recovery is removing his pants, which SpongeBob reluctantly does. However, the hook has got SpongeBob's underwear as well, and he is required to them off too, to which he refuses and is about to be reeled in by fishermen. To prevent his death, he grabs onto the Krusty Krab's clam sign as a means to remove the hook from his underpants, which results in them being ripped off and his naked body crashing into the Krusty Krab's doors, to the laughter of Pearl and her friends.
An embarrassed SpongeBob has learned his lesson and runs home, attempting to cover his crotch and buttocks in the process.