Content warning: This article includes an image of a severed cat tongue.
Humans may spend a third of their lives asleep, but cats can spend as much as half their time awake just licking themselves. Until recently, we didn’t know much about the mechanisms of this behavior or how tongue grooming helps kitties keep clean, cool their fur, and eradicate pests like fleas.
To learn more, Alexis Noel and David Hu, two scientists from the Georgia Institute of Technology in Atlanta, got intimate with cat tongues in new research published today in the Proceedings of the National Academies of Sciences. Their analysis was used to develop a new easy-to-clean hairbrush that may help pet owners with allergies, and could lead to advancements in cleaning tech and soft robotics.
Up close, a cat tongue almost resembles a forest of backward-facing hedgehog spines. These spikes are called papillae, which are made of keratin, the same class of hardened proteins that make human fingernails, horse hooves, and tortoise shells.
The researchers took a papilla from the severed tongues of six cat species—a domestic cat, a bobcat, a cougar, a lion, a snow leopard, and a tiger—cleaned them, and scanned them to create 3D models. All the severed tongues in this experiment were donated after death, so thankfully no cats had to die for this research.
What they discovered challenged almost three decades of cat tongue dogma that has described papillae as cone-shaped. They are actually scoop-shaped, the researchers found, with two hollow cavities: one at the base and one at the tip. These cavities create surface tension, allowing cats to wick and stabilize salival fluid, even if the tongue is upside down.
To test this theory, the researchers dried a severed cat tongue with a blow dryer and paper towels before weighing it. Then they dipped the tongue in water and measured the amount of fluid retained in the papillae.
They also built a motorized “automated grooming machine,” attaching the tongue to a horizontal rack and dragging it at varying speeds across a chunk of fur from the same dead cat. The experiment was repeated with blue food dye to determine the distribution of saliva.
It turns out that the length of papillae plays a central role in feline hygiene. Cat fur has two layers: a topcoat for protecting against the elements, and an undercoat for regulating temperature. Papillae gets saliva to the base of the fur — without it, cats would only be able to clean the top layer.
“The caracal, cheetah, and leopard are the most ‘groomable’ cats due to their short, sparse fur,” the researchers wrote. However, two Persian breeds were deemed “ungroomable” thanks to hair so long that the papillae can’t reach the base. This is why Persian cat owners must groom their pets daily and bath them monthly, or else their fur will become matted and greasy.
Using their 3D models, the team created a tongue-inspired grooming (TIGR) brush that is 400 percent larger than domestic cat papillae. They attached this device to their grooming machine and raked it across faux nylon fur. The TIGR was more effective compared to a human hairbrush, and also much easier to clean.
Because this device gets lower into the fur, it could be used to apply medications or cleaning mixtures directly to cat skin, potentially allowing people with allergies to coexist with cats — a better alternative than allergy shots, pills, or daily cat baths. The researchers have filed a provisional patent for this new technology.
The scientists suggest this tech could also be used in soft robotics or other situations that involve cleaning flexible filaments, such as carpets. Experimenting with dead cat tongues may seem weird, but it turns out felines still have a lot to teach us.