Cats are often humorously described as "liquid" because of their incredible flexibility and ability to squeeze into tight and unusual spaces, flowing into shapes much like a liquid would. This concept has been popularized in videos and memes showing cats contorting their bodies to fit into small containers and spaces, defying the typical rigidity expected of solid objects.
Scientifically and physically, cats are not literally liquid but are exceptionally flexible mammals. The phrase "cats are liquid" is more a playful observation of their unique body structure and behavior, rather than a literal statement. Additionally, "Cats Are Liquid" is also the title of a popular 2D platformer game series featuring a cat character with liquid-like abilities, which further showcases this cultural meme in a creative format.
Thus, while cats are biologically solid animals, their physical agility and behavior often make them seem almost liquid in nature in a humorous and metaphorical sense.
