The definition of a liquid is "a material that adapts its shape to fit a container." Although we commonly think of liquids as items like coffee and beer, all observations seem to indicate that cats are also liquid. But how do they fit into spaces that they're larger than? How do cats seem to compress into whatever shape?

There are a few anatomical and physical reasons.

First, cats are super flexible. A cat’s front legs are attached to their shoulder via a very small, free floating clavicle (collarbone) by only muscles, not bones. This allows them to fit their bodies into tiny spaces, because their neck and shoulders can literally be squeezed to spaces tinier than you'd imagine and can be compressed through a hole or a tunnel. Cats are designed to want to hide in small spaces for safety and hunting reasons; then, when they spot their prey, they immediately race to catch them.