Why is ketchup so hard to pour?

Ever go to pour ketchup on your fries...and nothing comes out? Or the opposite happens, and your plate is suddenly swimming in a sea of red? George Zaidan describes the physics behind this frustrating phenomenon, explaining how ketchup and other non-Newtonian fluids can suddenly transition from solid to liquid and back again. [Directed by TOGETHER, narrated by George Zaidan].