The Ig Nobel Prize: Why Are Cats Liquid? (2022)

>The Law of viscosity states that a fluid flows at a speed proportional to the force that is applied, where the constant of proportionality is the viscosity. Because ketchup does not obey this Law, it is known as a non-Newtonian fluid.

https://www.futurity.org/ketchup-physics-rheology-1321922-2/

Maybe you are thinking of those (starch based) mixes like ooblek that are shear thickening whilst ketchup (and mayonnaise, and similar) are shear thinning, but both are non-Newtonian:

https://en.wikipedia.org/wiki/Non-Newtonian_fluid

> Sometimes you just can’t get the ketchup out of the bottle, but after you shake it, it becomes runnier and therefore easily gets out.

should say "as you shake it" not after, since the decreased viscosity effect only lasts as long as the stress