In the wild, without human interference, when do cats purr? I wonder.
When they are happy, when they are sad. When they feel good, when they don’t feel so good. When they don’t hurt, when they do hurt.
Not only do we not know why or when they purr. We don’t even really know how they purr.
When they are happy, when they are sad. When they feel good, when they don’t feel so good. When they don’t hurt, when they do hurt.
Not only do we not know why or when they purr. We don’t even really know how they purr.
What lonesome loser said is borne out by this cite. Another popular article giving a bit more background.
They purr when their defenses are down. It’s a signal that that they’re open to being approached by another cat.
I also like lonesome loser’s answer. Pet them they purr. Scarlett purrs when we fight, and we fight HARD. She hisses, scratches, growls and purrs through it all.
Thanks, Q.E.D.!
By the way, a former member here was from Prince Edward Island, and used to be amused by “Fixed link” posts and Moderatorial edit comments, since that’s the popular usage for the (fairly new) bridge connecting the island to New Brunswick.
Which one? The first one or the second one? 
It should also be noted to the OP that the BIG cat species, most of them do not purr period. In fact there is only one species that does. I can’t remember which one it is though. I’m thinking maybe the Leopard or the Cheata…
Schrodinger cat can also bite and purr simultaneously.
Cats seem to purr when they want attention, mostly when they’re happy, but also when ill or injured.
Many queens purr when giving birth.
According to the sign on the wall at Brookfield Zoo, a cat can either roar or purr, but no cat can do both.
I have heard that some cats will purr when feeling threatened or otherwise unsafe. It’s speculated that in such instances the purring may be an attempt at self-soothing.
My hyperactive cat purrs most often when I’m in bed (sleeping or just about ready too) and he wants to sleep or lie on my head.
I read somewhere (sorry, no cite - but it was in a legit book about cats, not on the bathroom wall) that a cat’s purr can be somewhat equated with the human smile; sometimes we smile when we’re genuinely happy, but other times it’s more of a social convention to put others at ease. Sounds like a damn good analogy to me, from my experience with cats.
Do you lie on your head when he wants you to? 
Similar info from the SD Zoo: Home | San Diego Zoo Animals & Plants
My recollection is that the only big cat that purrs is the cheetah. A friend of mine had the opportunity to pet one when he travelled throughout Africa a while back and he said it was purring up a storm.
This place: http://www.szgdocent.org/resource/aa/cats/a-cat2.htm
Claims that cheetahs and pumas can purr.
Big cats can generally purr in one direction (I can do this as well, my g/f likes it), sort of a throaty “Chuff” noise on the exhale.
And, I assume, do one or the other or both while possibly being dead. Or not.
It’s my understanding purring has to do with communication between a mother cat and her kittens. Which is why it’s continued more in domesticated cats, as we’re their permanent mother cats.
And therefore it signals approachabilty…due to trust and contentment, or to distress and a desire for help.
Well, I don’t know but it made sense to me.
For the record, “big cats” as anything but a size term refers to genus Panthera, including the lion, tiger, leopard, jaguar, etc.
The cheetah is in genus Acinonyx, and only a kissing cousin to the other cats, big or small.
The cougar (puma, mountain lion, catamount, etc.) is Felis concolor, and despite its size is classed with the “small cats” in genus Felis.
Add to previous post: I can verify that cougars do purr; the local zoo had a cougar on exhibit while I was growing up, and we became as good friends as a zoo animal and a frequent visitor to his cage can become. He would purr when I came up and talked to him.