Examples:
https://www.aalaslearninglibrary.org/fileupload_content/Course279/cat_rub_chin.jpg
So, how come there’s a kitty G-spot under the chin? It’s near universal for cats to strongly like rubbing there so there must be something about the structure of the cat that happens to produce that effect or some source of utility.
WAG - It’s where its scent glands are located. I guess this bc I thought cats rubbed people to confer scent onto them.
Cats can’t reach that area with their tongues, so it’s much harder to groom. Cats enjoy getting their whole faces scratched and petted, in fact, and they also enjoy getting scratched right between the shoulder blades. Grab the nearest friendly cat and give it a good scratch between the shoulder blades, and you’ll see an expression of pure bliss. That is another spot that’s hard to groom.
One reason to keep more than one cat is because they love to groom one another, and will spend a lot of time doing this.
Oops. Sorry for responding to a GQ without knowing anything (well, technically I respond to all posts that way). It’s 3 am where I live and I’ve been working since 7am. That’s my excuse.
Ah ha! I knew mentioning cat pics would get me quick replies. Perhaps I should promise cat pics in every thread I start, cat-related or not.
First test subject was sitting in my lap as I read Bodoni’s experiment instructions. Subject responded with mild purring and looking at me with a “What are you doing?” expression.
Second test subject started mild purring and then got back to sleeping position.
Third test subject started mild purring and looked a bit confused.
Cats possibly defective.
The chin is one of the best parts of your cat. Use it regularly; you both will enjoy it.
Clearly, you need to do more testing on more cats.
Just a WAG, but…
As kittens, their Mother groomed them. Mother groomed them all over, including under their chins. As adult cats, they can look after themselves, but they have a problem grooming under their chins. So, stroking under their chins reminds them of when Mother was looking after them.
Similarly, cats love being rubbed at the base of their tails. Mother groomed them there as kittens, to encourage them to defecate. While they won’t eliminate on demand any longer as adults, they still love it.
In short, it reminds them of Mother Cat’s care. As you stroke them, under the chin or between the ears or at the base of their tail, they forget they are adults, and they are once again kittens, in the safe and reassuring care of Mother. You may not be Mother, but you remind your cat of her.
As I said, just a WAG, but my experience with my cats would bear it out.
My cat loves it anywhere on and around his head, neck, face, chin, and shoulders; he’ll gladly let you do that all day long. But you touch him anywhere near the base of the tail more than briefly and incidentally, and there WILL be blood, and then he’ll look at you like you’re some sort of retard for daring to do such a thing!
It isn’t just cats - my Aussie loves to have her chin scritched. But she doesn’t purr.
This explanation makes sense to me, but my WAG was always that animals like having their weak points touched by someone (or something) they trust. Some cats (maybe not all) like having their bellies scratched, as do dogs and even my friend’s rabbit. Of course if they don’t expect it or don’t trust you they’ll jump and possibly attack you. The same is true of humans. We have sensitive parts that are not obviously sexual yet are almost universally erogenous zones, under the right circumstances. The neck and thighs come to mind, and both of course have a lot of blood vessels running through them. Our bellies are also very sensitive, but a bit higher, where we have a ribs underneath, not so much (taking breasts and nipples out the equation). These are also places that will make you jump the most if you’re touched there without warning. It makes sense that these places would be more sensitive to surprise touch and could therefore also be more sensitive to pleasurable touch.
The glandular tissue associated with the head produce “Feline Facial Pheromones” that are associated with bonding. They tend to have a calming effect and facial rubbing and pheromone exchange is a common bonding mechanism among friendly cats. Synthetic versions are used in products like Feliway to calm cats.
The Supracaudal/Violet Gland on the other hand is more purely associated with territoriality. Not necessarily hostile, but it does not serve the same bonding function. It is a sensitive area that in unfixed male cats in particular with all that coursing testosterone can sometimes develop the condition “stud tail” when the gland become hyperactive.
Y’all might be right, but I’d sure like to see some better evidence than just kute kitty pix and speculation. After all, this is GQ. Any cites to bring forward?
My cat is my cite. 
The patches between the eyes and ears ( which are only lightly covered with fur ), the lips, and the chin are all richly supplied with glands producing fatty secretions…Studies of feral cats have shown that rubbing by one friendly adult against another is commonplace in well established groups, but is particularly likely to be expressed by a subordinate individual towards a dominant one ( see Chapter 6; Macdonald et al., 1987 ). David MacDonald ( personal communication ) suggests that a pet cat rubbing on its owner behaves as it would towards a dominant cat and is, therefore, like a pet dog fawning and tail wagging to a human.
From chapter 14 ( Bateson and Turner ) in The Domestic Cat: the biology of its behaviour ed. by Dennic C. Turner, Patrick Bateson ( 1988, Cambridge University Press ).
This relates more to cats rubbing on us, but I trust is also cite for inter-cat behavior and why they might find it appealing to be rubbed by us.
That’s a step in the right direction, but still involves considerable interpretation and assumption, supported by your phrase “I trust.” My cat looks happy while rubbing, but is that “smile” really the same as a smile on a human?
Every cat book I’ve ever read mentions the scent glands along a cats jaw and on the top of it’s head. These are the same scent glands it uses to mark territory and communicate with other cats. Since this communication is beneficial to survival, it’s reasonable to assume some sort of reward mechanism would have evolved to encourage this. It was likely enhanced in the domestication process as people seem to prefer cats that can be so easily pleased.
Welcome to the wonderful world of animal behaviorism :). At a certain level you have to interpret.
Who’s to say ( other than we can pretty securely assume there is no higher function intellectual contemplation going on ). They seem to enjoy it. Why?
1.) Could be reenforcing social bonds in a catlike fashion as above.
2.) Could be reaching harder to groom areas, which the cat finds pleasurable as a cleaning function OR reminds them of being groomed by mom, which generates “happy thoughts.”
3.) Could be pleasurable sensory stimulation as a result of greater nervous enervation due to the presence of all that extra glandular tissue.
4.) Could be any or all of the above.
I figure it is most likely at least #1, but could be all of the above because:
A.) We know from dissection that the area is heavily glandularised and…
B.) We know from observation that mutually friendly cats rub their faces against one another as a form of social discourse.
Can you prove that’s why cats like to have their chins scratched? Well, no - you pretty much have to infer it. I don’t think it is possible to go much farther than that.
ETA: 5.) Or maybe they’re just lazy and appreciate it when we manually do all their scent-marking of us for them.
Maximally inapposite username/post combination. 
I’m kind of surprised we’ve gone this far in the thread without finding a scholarly article on the topic. Certainly, some animal researcher has noticed this and tried to figure it out.
Shoot, I certainly don’t see one, except for one that mentions kitty acne. However, no kitty I have had has acne and they all love the chin scratch.
