Eric F. Brown over at "The Rheol World" has a new post of the guys from "The Big Bang Theory" having fun with Oobleck (cornstarch and water) on a music speaker. Sheldon Cooper does an adequate job of describing the phenomenon - it's not a complete description, but he certainly is not incorrect in anything he says.
Compare this with this awful video, only 6 seconds long and (about that many words too) which makes a total mess of the matter:
Oobleck is not thixotropic; it certainly shows signs of rheopexy, dilatancy and other non-Newtonian behavior, but not thixotropy.
This is another example of something I've discussed before: while the word "thixotropic" sounds like "thick", that association is completely inaccurate when it comes to understanding the meaning of the word. A thixotropic material will reversibly reduce its viscosity at a constant shear rate. When the shearing stops, the viscosity increases. The imaginary word "thinnotropic" would be closer to its true meaning.