non-Newtonian liquids aren't your regular liquids. There are various types, all exhibiting different patterns of changing viscosity. Some behave like solids when stressed, and others more like liquids. Space Pen ink, and paints that stick to a brush when at rest but glide on easily when the brush is applied to a surface behave more liquid when stressed.

Some pretty common substances are non-Newtonian: ketchup, blood, yogurt, gravy, pie fillings, and cornstarch paste don't follow the normal liquid model. This is also why you don't want to struggle when you inevitibly get stuck in quicksand.

You can do some pretty weird stuff with non-Newtonian liquids. Excitable game show hosts can walk on them.

Common old cornstarch mixture, also known as an Oobleck is the DIY version of a non-Newtonian fluid. You can make it behave in a truely disturbingly organic fashion. Monsters are made of this. Mix up some cornstarch and water, put a metal tray on top of a sub-woofer, hold the tray down, and watch the fun.

Or simply mix some Oobleck in a bucket. Put your hands in, and it's a fluid. Punch the surface of the liquid, and it'll be a solid. Kind of like a liquid version of silly putty, which is also non-Newtonian.