Are Cats Really Liquid? The Science Behind the Joke

By Dr Duncan Houston

A cat curled into a small box can look as though someone poured it there. Paws disappear, the back rounds and the outline seems to match the container almost perfectly.

The “cats are liquid” joke has inspired both a playful physics paper and serious research on how cats negotiate openings. The useful distinction is between looking fluid and literally changing state. Your cat is still an animal with a skeleton, muscles and physical limits.

Quick Answer

Cats are not literally liquids, but their flexible movements and changing resting shapes make the comparison entertaining. A humorous rheology paper used cats to explore how observations depend on timescale, while separate behavioural research examined how cats approach small openings. Neither gives owners a reason to force a cat into a container or assume every narrow gap is safe.

Where the liquid-cat idea came from

In his 2014 paper On the rheology of cats, physicist Marc-Antoine Fardin applied the language of flowing materials to familiar cat photographs. The paper plays with a simple observation: a cat can appear to hold its shape in one moment and gradually settle into a very different outline in another.

Rheology studies how materials deform and flow. One concept in the paper compares the time a change takes with the time over which it is observed. That is a real physics idea, used here in a deliberately humorous setting.

The paper did not establish that a living cat switches between solid and liquid tissue. Treating its jokes about jars, flow and relaxation as a veterinary experiment would miss the point.

Looking fluid is different from being a fluid

A cat changes posture actively. It bends, tucks its limbs, turns and chooses where to rest. Fur can also hide the outline of the body, making a curled cat look more shapeless than it is.

The contrast is easy to see in ordinary life: the same cat that curls into a bed can stand up and walk away. It has not solidified. It has changed position.

Likewise, the label “non-Newtonian fluid” is part of the internet joke, not a practical description to use when deciding how to lift, handle or house a cat. You cannot infer that a cat can safely be compressed because a photograph looks amusing.

What opening-size research actually found

A separate 2024 study, Cats are (almost) liquid!, tested companion cats with openings that changed in width or height. In that setting, cats approached narrow tall openings differently from uncomfortably low ones.

The researchers interpreted the behaviour in terms of trial-and-error and body-size awareness. This was a study of movement decisions, not proof that cats understand a concept of their own “liquidity”.

It also does not mean every cat will accurately judge every gap. An opening in a research setup is different from a moving recliner, a partly open window or the space behind an appliance.

Why a small resting place can appeal

A box or covered bed can offer a place where a cat is partly concealed and can rest away from activity. The AAFP/ISFM environmental-needs guidelines include access to a safe place among the core needs of cats.

The important part is a usable choice. A cat should be able to enter, turn as needed and leave without being trapped or handled into position. Some cats prefer an open bed or a high perch; choosing something different from a viral video is not a failure of feline flexibility.

In a multi-cat home, consider whether another cat can block the entrance or the route out. More than one resting option can be more useful than one especially attractive box.

Offer a box, not a squeezing challenge

Start with a stable, roomy cardboard box on a secure surface. Remove staples, loose packing material and anything the cat could become caught in. Keep the opening easy to use and let the cat investigate voluntarily.

Watch the actual choice. Does the cat settle, move elsewhere or use the box only as a brief hiding place? You can try a different location or style without progressively shrinking the available space.

• Avoid jars, narrow-necked containers and unstable glassware.
• Do not press down on the cat or tuck limbs inside for a photograph.
• Keep lids and handles from closing around or catching the cat.
• Place resting areas away from machinery, hot surfaces and places where doors may shut.
• Check a new box as it wears, especially if it becomes torn or collapses.

The aim is comfortable resting and choice, not proving how small your cat can become.

Check household gaps before the cat does

Look behind and beneath furniture, around appliances and near storage areas. Consider what moves, closes or heats up, as well as the opening itself. A space that can be entered may not have an easy route back out.

Do not rely on the rule that if a head fits, the rest of the body must safely follow. The shape of the opening, the body and the surrounding equipment all matter.

Before using a washer, dryer or movable chair, check where the cat is. Close off unsuitable spaces and provide an appealing resting place elsewhere. A cat's curiosity is a reason to improve the setup rather than to leave a risky gap available.

Keep flexibility separate from health assumptions

Their flexibility comes from healthy joints and muscles, so stiffness or reluctance may signal arthritis or pain. Monitor stretching and flexibility: limits or pain may need veterinary check-ups.

That caution is a reason to notice changes in ordinary movement, not to test the cat with increasingly awkward spaces. Cornell's information on slowing down and joint problems explains why movement changes deserve attention.

Common mistakes

• Reading a humorous physics paper as proof that cats have no physical limits.
• Copying a narrow-container photograph rather than providing a comfortable resting choice.
• Assuming a cat's willingness to enter a gap proves it is safe.
• Handling the cat into a pose or blocking its exit for a video.
• Using a flexibility challenge to judge whether a cat is healthy.

Frequently asked questions

Are cats really non-Newtonian fluids?

No. That is a playful comparison. A cat changes its posture and moves under its own power; it does not become a different state of matter.

Why does my cat choose a box instead of an expensive bed?

The box may offer a preferred location or sense of enclosure. Offer suitable choices and observe what the individual cat uses.

Should I make the box smaller to provide enrichment?

No. Enrichment does not require an uncomfortable fit. Try a useful location, a different opening or a separate play opportunity instead.

Can all cats fit through the same gap?

No. Individual bodies, movement and the shape of the opening differ. Do not use another cat's video as a safety guide.

Enjoy the joke and improve the setup

A comfortably curled cat does not need a scientific label to be fascinating. Offer safe resting places, protect access to household hazards and let the cat choose its own shape.

ASK A VET™ encourages curiosity about animal behaviour alongside practical, cat-friendly choices at home.