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It’s a sauce you fool

Fun? Fact: Technically speaking, ketchup behaves more like a solid than a liquid. That's why it's a fool's errand to open a new glass bottle and hope to deliver a measure before your fries get cold, without involving some effort. It is considered a pseudoplastic, much like wet concrete or nail polish. It's viscosity changes with the application of shear force such as stirring, shaking or impact. That's why you either vigorously shake(cap on, please), or strike the bottle with your hand repeatedly, to temporarily lower its viscosity. Enjoy your fries.