The Rheology Of Cats

Relaxation time is the key:

Marc-Antoine Fardin was awarded the Ig Nobel Prize in physics for his research paper on the rheology of cats.

"At the center of the definition of a liquid is an action: A material must be able to modify its form to fit within a container," Fardin said.

In his official research paper, Fardin discusses many factors including relaxation time, experimental time, the type of container, and the cat's degree of stress.

The conclusion? Cats can be either liquid or solid, depending on the circumstances, Fardin reported in the Rheology Bulletin in 2014.