Non-Newtonian fluids are those which do not have a constant coefficient of viscosity. Fluids such as the popular science experiment nicknamed Oobleck become more viscous as force is applied, but not in a linear relationship with the force being applied. As you push on Oobleck, for example, it partially solidifies in response to the pressure. So you can take a lump of Oobleck, squeeze it in your hand so that it forms a ball, and then as you hold it in your hand you'll see the ball dissolve back into a liquid.
But that's a pretty basic (and easy to make) form of these fluids. It turns out that you can apparently also make a liquid substance that turns fingers mallet-proof!
Or at least that's what's shown in an an impressive demonstration over at Popular Science, which includes wrapping the goo around a person's finger and then banging it with a mallet. The material is created by a company called Tech 21, who takes this incredibly durable substance and uses it to create impact-resistant cases for smartphones and tablets.
While this may seem like a trivial application of this technology, it's just another example of the many ways advanced materials design can impact the world. It's easy to imagine that similar materials are being applied for helmets and various other forms of safety equipment, and there are already known safety applications for these advanced materials, in making vehicle travel over rough terrain safer.