A whoopie cushion is a practical joke device involving flatulence humor, which produces a noise resembling a "raspberry" or human flatulence. It first appears in the episode "Fools in April."
Whoopie cushions are made from two sheets of rubber that are glued together at the edges. There is a small opening with a flap at one end for air to enter and leave the cushion. In most episodes, they are red or pink.
To use it, a person must first inflate it with air, then place it on a chair or squeeze it. Some whoopee cushions can be self-inflating. If it is placed on a chair, an unsuspecting victim will sit on the whoopie cushion, forcing the air out of the opening, which causes the flap to vibrate and create a loud, flatulence-like sound.
Role in series
"Fools in April"
Mr. Krabs takes a seat on his office chair and hears a flatulence noise when he sits down. SpongeBob had put the whoopie cushion there as an April Fool's prank.
This is one of the novelty items offered by Frank when SpongeBob and Patrick are looking for the best gag in stock to prank all of Bikini Bottom.
Later in the episode, once Mr. Krabs shines the spotlight on the pair to showcase the "live nude pranksters" in the Krusty Krab as punishment for threatening to burn a dollar as well as pranking the entire town, an embarrassed SpongeBob tells Patrick in regret that they should've bought the whoopie cushion instead of the Invisible Spray.
After Squidward tells SpongeBob that excessive laughter will result in permanent loss of his laugh box, SpongeBob tries his best to control his laughter regardless of how funny the situation is. After getting off work, he encounters a whole street of whoopie cushions from a whoopie cushion truck and ultimately tries to avoid stepping on any of them, which fails, so he runs away to hide himself from the humor.