Billy stumbles upon the band Purple Filth, lead by the neighborhood bully. He requests to join but is turned down in favor of Grim, who is asked to play the electric guitar and is shown combining notes and chords.
Sheldon, Leonard, Howard, and Raj create an oobleck using corn starch and water. Initially, it's a liquid, but when they turn the music on, it resembles a solid. Sheldon explains the phenomenon to Penny: it's a non-Newtonian fluid which is liquid but becomes solid due to the percussion from the speaker.