Do they do it specifically because they need to vomit? Or is it a coincidence and many things make them vomit?
Having had cats that ate certain houseplants, then vomited, I thought that was the case. But now I have a cat that eats plants and never vomits.
Just when you think you can reach a conclusion about cats, one comes along and screws up the data.
Wikipedia isn’t much help here…
My personal opinion, from over three decades of living with cats, is that cats ENJOY horking, and will seek out grass so that they can hork even more.
Seriously, cats need to rid themselves of hairballs on occasion. I don’t know if they search out grass to help them hork or not.
I think cats start out by eating grass to vomit, but as they do this they actually develop a taste for it, so to speak. There are cats that love plants, of course they still eat meat, but it makes a nice addition.
I had a cat that LOVED aloe. She’s sink her teeth into the plant and suck out all the juice. I don’t know exactly why but she liked it.
Never had a cat but I’ve seen dogs do this many times. I asked adults when I was a kid that standard answer they gave is there is some kind of nutrient(?) they are deficient in and are getting it from “green grass” type things.
Could be just urban myth, don’t know.
Several leading authors on pets with some degree of respectability (Cleveland Amory’s books on cat care were my first source) have reiterated that cats typically eat grass (or house plants, in the case of indoor cats) to obtain folic acid, one of the B vitamins which is almost totally lacking in a purely carnivorous diet but common in most green vegetables (including plant leaves/blades). After the folic acid is extracted by action of stomach juices, though, the cats, unable to process the green stuff for other nutrients due to having the short carnivore digestive tract, will vomit up the detritus. Since it also acts as a purgative for anything “stuck” in the stomach, such as hairballs, there may be a double function.
I report this, by the way, in the “something I read in a usually reliable source” category of unsubstantiated information, and would welcome a veterinary science person validating or refuting it.
My sister had heard it was good for cats for some reason or another that she couldn’t explain. I retorted that it was just something they did to vomit and gave her a few Google results to corroborate.
In either case, she wanted to buy indoor grass for it (a product she had seen advertised somewhere) and I didn’t want her scraping up cat spew unnecessarily. She has a new cat, originally intended to chase off mice, now there to give her something to coo over :rolleyes:
Our cat, indoor only, loves grass. We buy it in little packages labelled “cat grass” and grow it for her. We call it her salad. She seldom horks, though.
We were also surprised to see the canned cat food here in Budapest contains carrots, beans and peas. 
She does NOT eat carrots, beans or peas, but she keeps that grass mowed!
I bought one of those Chia cat grass things and let the grass grow to about 3 inches tall. It took my 2 cats less than an hour to devour it all. A few hours later my older cat horked up a massive lump of the grass and hair. The kitten left me some green turds in the cat box for a few days.
This guy, he lives in my neighborhood, and he heard from a friend of a friend about this other guy who’s had a lot of cats, and this other guy apparently says they eat grass just to purge. So that’s settled.
Desmond Morris in Catwatching gives this as ‘the most likely explanation’.
My Katya likes to eat pet grass, and doesn’t vomit afterward. I think she just likes the taste or the texture or something.
Mine like their cat grass. Neither horks after eating it. I also tend to keep them brushed regularly which reduces the occurrence of hairballs for them.
Incidentally, they are on a limited ingredient diet that only has duck and peas, so they are getting a green vegetable from their kibble.
I learned a new word today.
I say “harf” instead of “hork”.
Budget tip- get live wheatgrass at grocery store for 1/2 price of catgrass at pet store.
I have read that cats eat grass to supplement their diet with things they are otherwise missing, and that earlier in their evolution this need was met by eating the full digestive organs of their prey animals.
^^ I guess that means many housecats have stomachs that aren’t user to that kind of food, so it reacts negatively, leading the them puking?
What I wanna know about is how my cat’s very finely tuned internal clocking mechanism works so that she knows to only hork indoors, never outside. We let her outside (on a harness, and only when we’re out there working in the yard) and she binges on grass to her heart’s content. Then, invariably, 15 minutes after we all go in, up comes the nasty.
I can leave her out there for hours, waiting for the horking to commence so that we can go in without needing to clean anything up, and she just lays about, enjoying the sun. I can leave her out there for only 15 minutes, not even enough time to eat a blade of grass. But always, without fail, hork-hork-hork on the carpet.
I can deal with the puke, but why can’t we do it outside?!