The ketchup is ordinary but it becomes more slippery once you apply shear stress to it. So it's a thick syrup when it's stationary but once you apply a shear stress such as squeezing it, it become slippery, hence it's viscosity decreases. Viscosity can be explained as how slippery the layers of a material are in reference to each other. Newtonian fluids stay the same; their viscosity does not change, no matter how you stress the material viscosity is constant. But ketchup in this case is called a shear-thinning fluid, apply a stress to it, it's less viscous.

@@harley6659 thank you for your explanation!

that is very clever LMAO