http://www.straightdope.com/classics/a1_009a.html
I find no one as noted that cats who spit hairballs live enclosed in their “owners” houses. Cats that aren’t pets or are allowed outside whenever they want (by outside i mean countryside, not a urban environment) are never to be seen spiting hairballs. They eat some type of wild grass type leafs that seems to avoid hairballs. For some years these plants are sold specifically for this purpose allongside cat food…
I imagine that diet is a fair part of this, as well - I imagine that a feral feline would ingest enough fat from whatever he is eating to “lube the works,” as it were.
A dollop of petrolatum on the toungue will usually cure a hairball problem & lead to recycled cat food in the place of wild mouse fat.
Back when we used to let our cats go outside whenever they wanted, in our suburban neighborhood, with woods on 2 sides and a vacant lot on a third, the cats still seemed to do the hairball thing on occasion. In fact, they would go outside, eat some crabgrass, and then upchuck. Sometimes they’d insist on coming inside first so they could vomit on the carpet instead of on the nice clean grass. 
I’ve found this in Google Search as i thought no cat would vomit after eating this grass:
Here’ssome material from Levy’s herb book that basically says what we already know, but confirms the idea that we shouldn’t stop them from eating it: “Cats should be encouraged to eat any green herb, particularly couch grass (also known as twitch, crab grass, dog grass), that common weed and a basic internal cleanser for the carnivores, used as a laxative or to induce cleansing vomiting.” In another section of the book “this grass is so important for maintaining health in dogs and cats that, if not available as a wild plant, roots should be procured and planted where dogs and cats can utilize them.” http://www.holisticat.com/grass_arch1.html
I don’t know if it’s a good source, but if it is the crabgrass can be laxative also, as i never seen any of my cats vomiting after eating grass or spiting hairballs, i guess maybe they never eat too much of it…
IME, allowing cats to eat grass (indoors or out) does induce vomiting, which in turn clears out hair in the stomach and esophagus before is becomes a hairball.
Outdoor cats do vomit–they just do it outside when no one is watching.
Grass-induced vomit is typically very thin and liquidy, which also means that it is coughed up quickly (unlike the hairball that an indoor, long-haired cat can take hours to cough up), and virtually invisible.
It may be so. But with the four cats i allready had (one in present time) i never witnessed vomiting or even coughing just after the grass was eaten. At times my cats have to remain inside, when sick or 1-2 whole days so a medicine can act eficiently to prevent flees, i give them some fresh leafs of grass to eat and i never see them vomit, or coughing as imediate reaction. I have seen them coughing, sure, i have even seen them vomiting but for other reasons, something they ate or when sick (no fur in vomit, just undigested food).
I even went and watch at some crabgrass photos, though maybe it was an american plant nonexistant here in Portugal but found it’s the same and that this grass was taken to America by the English to feed cattle.
The main point was: no, cats haven’t tame us to wipe their vomit as a need. In more ideal environment cats do just fine with the grass…
Bwah?
I’ve had my share of outdoor cats, and every last jack man one of them spat up hairballs like it was going out of style.
My current cat, who is entirely indoor now that I’m living in “The Big City”, never, ever spits up hairballs.
Very cat-like… It’s a love/hate relationship, fer sure.