Blood, lymph fluid and other biological liquids can have surprising and sometimes troubling properties. Many of these biological solutions are non-Newtonian fluids, a type of liquid that is characterized by a non-linear relationship between stress and strain. Consequently, non-Newtonian fluids don’t necessarily behave as one would expect from a liquid. For example, some of these peculiar fluids deform when touched lightly but will act almost as a solid when a strong force is applied.