I’ve been licked by both cats and dogs, and a dog’s tongue is much smoother than a cat’s tongue.
Is there any reason for that difference, or is it just a fluke of evolution?
Cats have hygiene standards. They use their tongues to comb and groom their fur. The bristles on the tongue help with that.
Dogs love their stink and have little need for grooming. The grooming they do do is mostly with their incisor teeth.
Cats use the spines on the tongue to transfer water when drinking, they don’t curl the tongue the way dogs do. The rough surface also helps remove flesh from bones.
Which reminds me of this famous Mailbag item:
Why isn’t a dog’s tongue rough as well, if it confers a great advantage in eating meat?
Grooming:
researchers are discovering more about what that [cat] tongue, with its hundreds of tiny, backward-facing spines called papillae, is doing.
In a new study published in the journal Proceedings of the National Academy of Sciences, researchers at Georgia Tech found that papillae are not cone-shaped and solid, as previously thought, but instead scoop-shaped and hollow.
“It allows the cat to store and hold saliva in these tiny little spines,” says Alexis Noel, a researcher at Georgia Tech. She and her colleague David Hu used high-speed video and CT scans to observe how the papillae on a cat’s tongue wicks saliva from its mouth onto its fur.
Dogs can chew on the bones in a way that a cat can’t. Bigger jaw, stronger jaw muscles.
“Cats aren’t clean. They’re just covered in cat spit.”
Dunno where I heard that line (I didn’t come up with it!) but I think of it every time I see a cat grooming itself.
Many features confer advantages to carnivores and they all share some of them but not all of them. The cat’s tongue will be built on numerous evolutionary steps that separated cats and dogs from their ancient common ancestor. Parallel or convergent evolution does sometimes occur so that different species end up with the same kind of specialized features. But look at all the differences between cats and dogs, most of the similarities are very general and even shared with humans and most mammals, but it is the differences that identify the species.
Reminds me of Terry Pratchet’s take on cats:
“If cats looked like frogs we’d realize what nasty, cruel little bastards they are. Style. That’s what people remember.”
Right, like “Four score and seven years ago” compared to “Mission accomplished!”
Fixed that but is a really funny typo.
This is also why cat allergies are more common than dog allergies. A lot of people are allergic not to the fur, but to the saliva.
One oddity: I have two cats, an 11yo spayed female Siamese mix (Allie) and an approximately 7yo neutered male basic generic cat (Buddy). Allie’s tongue is MUCH scratchier than Buddy’s (they both tend to lick the human petting them).
Allie’s fur is also much thicker, since she’s been a pampered indoor kitty her whole life and Buddy’s spent at least a couple of years as a community cat surfing among friendly humans (he recently apparently decided to just move in with my household).
Wondering if gender or fur thickness has anything to do with it, or just individual variation.
According to this article, Why Are Some Cats Tongues Rougher Than Others? some cats have a ‘soft tongue’ as a result of a harmless mutation.
Concur. Cats are extremely efficient hunters (as well as being malicious little bastards towards their prey) and just like to show off. They kill because it’s fun.
If cheetahs behaved like house cats, they’d run at top speed EVERYWHERE…just to show that they can do it.
And yet, I notice your avatar is… 
Dogs are like toddlers. Cats are like teenagers.
Yes. Perhaps the best cat I ever had. He walked out of the woods one day as an adult in terrible shape. Gained weight to 17 pounds and became absolutely fearless. He held off wandering dogs, brought frogs and snakes into the house, and, yet, was also the cuddliest cat imaginable. His cremains sit in a black and white ginger jar on my bookshelf next to my favorite portrait of him.