The observation that a cat can perfectly occupy a shoebox, a vase, or a kitchen sink has become a widespread internet phenomenon. Felines conforming to the exact shape of their containers raises the question: are cats actually a liquid? This humorous concept has a foundation in science, prompting a look at the physics of material states and the unique biology of the domestic cat.
What Defines a Liquid
The classification of matter into solid, liquid, or gas relies on specific physical properties. A liquid is defined as a state of matter that possesses a definite volume but lacks a fixed shape. This characteristic means a liquid will flow and readily adapt to assume the shape of any container it is placed within.
Liquids maintain a consistent volume because their molecules are closely packed, making them nearly incompressible. Unlike a solid, the particles in a liquid have enough energy to move and slide past one another. This freedom of movement allows a liquid to flow under gravity and fill the bottom portion of its vessel.
Feline Anatomy and Flexibility
The visual comparison of a cat to a liquid is made possible by an exceptionally evolved anatomy designed for agility. The cat’s most significant adaptation is its spinal column, which is noticeably more flexible than that of many other mammals. While humans possess 33 vertebrae, a cat typically has around 53 vertebrae, including those in its tail, with a greater concentration in the lumbar and thoracic regions.
These individual bones are not rigidly bound by strong ligaments; instead, they are held together by muscles, which permits a much greater range of motion and rotation. The cushioning discs between each vertebra are highly elastic, allowing the spine to compress, stretch, and twist with remarkable ease. This structure lets a cat rotate its body nearly 180 degrees, mimicking the deformation of a fluid.
Another element contributing to this apparent fluidity is the cat’s unique shoulder structure. Unlike humans, whose clavicles anchor the shoulder to the rest of the skeleton, a cat’s clavicle is vestigial, meaning it is very small and free-floating. This lack of a rigid bony connection means the shoulders can collapse and compress inward.
The ability to fold the shoulder structure allows a cat to squeeze its body through any opening that its head can fit through. Furthermore, the skin itself is loosely attached to the underlying muscle layer, which permits considerable lateral movement and stretching. This elasticity allows the cat to shift its shape and volume to fill tight spaces without resistance, completing the illusion of a pliable, shapeless substance.
The Physics of Cat Flow
The question of whether cats are a liquid has been formally addressed in the field of rheology, the study of how matter flows and deforms. French physicist Marc-Antoine Fardin explored this concept, centering his analysis on relaxation time. Relaxation time is the duration required for a material to adjust its shape in response to an applied force, such as gravity pulling it into a container.
If the time spent observing the material is longer than this relaxation time, the material behaves like a liquid. Conversely, if the observation time is shorter, the material acts like a solid. By this rheological metric, cats can be classified as liquid under certain circumstances.
A cat observed slowly sinking into a bowl or perfectly filling a box over a period of minutes has demonstrated a short relaxation time relative to the observation period, thus acting as a fluid. Fardin categorized felines as an “active rheological material” because their internal state, such as whether they are awake or asleep, impacts their “viscosity” or resistance to flow. The cat’s ability to transition between a rigid solid and a perfectly conforming liquid is what makes the viral concept scientifically provocative.