The Whirly Brain is a flying brain with eyes, a long stem, and a propeller on the top. The toy's box contains a monster mask to scare someone so you 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.
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.