The Whirly Brain is a flying pink brain with eyes, a long stem, and a propeller on the top. The toy's box contains a monster mask to scare someone so one can connect the propeller to the brain to play with it. The Whirly Brain can also produce brain gas out of the stem by pressing the button on the remote control.
Role in series
SpongeBob and Patrick buy Whirly Brains at the Bikini Bottom Toy Shop after watching an advertisement on television. They use the Whirly Brains to play pranks on Squidward, Mrs. Puff, Mr. Krabs, and several other Bikini Bottomites, until a kid challenges them to a race, but as they play, the Whirly Brains end up getting stolen by a grouchy old man who keeps them in a barrel. With Sandy's help, the Whirly Brains are returned.
The old man explains that the reason why he stole them was because he was jealous of seeing kids having all the fun and wanted to experience flight. SpongeBob and Patrick decided to donate the Whirly Brain propellers to the old man and he happily flies around in the air.