Cornstarch and water make a remarkable mix. Treat it gently and it flows, handle it roughly and it shatters like a solid. In this video you will see a rotating cylinder being placed in cornstarch and water. The cornstarch mixture is so thick that the cylinder stalls; however, vibrations from a loudspeaker cause it to become sufficiently fluid that the cylinder will once again rotate. When the loudspeaker is on, the cylinder rotates; when it is off, the cylinder stalls. Prof. Itai Cohen explains what is going on.