haha ive actually seen throw up in our cat dishes too...wow. Yeah i heard cats ate grass when sick but i heard it makes them puke too. He does eat any type of ribbon/string he can find.
Grass can be used as a vomit inducer, however grazing is a natural part of their diet, and does not always cause vomiting. Cats tend to use grass as a cure-all for stomach ailments, so it's good to have it on hand.
My female cat has always had a very sensitive tummy- she has a tendency to vomit in the cat food bowl as she is eating and it's not as if she overeats- she is a muncher- lot's of little meals a day. I saw an ad for the Iams sensitive stomach (the pink bag) and she has been doing wonderful on it and refuses to eat the other dry food unless she has to. You might try that. Oh- doesn't grass make cat's vomit? At least that's what mine usually do- brats.
If it isn't parasites, then most likely he just has a picky stomach. That's not uncommon. (Check on that 'Red 40' thing.) To help him settle his stomach, you might consider going to the nearest patch of grass and picking some, taking it in and rinsing it, then offering it to him alongside the food.
You could also go the route we did if you want and buy one square of sod from the local greenhouse. (It usually runs less than a dollar) then growing it in pots for the cat to graze on at will.
Oh he doesnt have parasites. We have giving them this liquid worming med that you put in their food. Its not that. and theres none in the litter. I dont know but i think he might just have a sensitive stomach?! haha ramen noodles..my bf actually eats them, i refuse! Im very picky. Its not that we absoultely cant afford it because we can. Its that im not working and well my bf is very tight with his money. If we felt the cat was in dire need of a vet we would def take him. My bf seems to think he just over-eats.
Have the hard foods you've provided had 'Red 40' in them? Mine are all very sensitive to that food-dye and we have to look for foods that don't have it. Purina One has a really good dry food without the dye, and it's still in a 'grocery-store-diet' price range.
I think Savas may be onto something when he mentions parasites. If a change of food doesn't handle the problem, you might consider buying a bottle of wormer, but really (and I am reluctant to say this on virtue of it being a little gross) check out their litter box and their rears for a few days to see if you notice the presence of parasites transferred from their gut to the faeces or their fur.
You may just decide to worm them anyway for good measure, which is fine, but please be very careful and read the instructions on the package and DO YOUR FOLLOW-UPS. Most wormer meds will ask you to dose the cat, then ten, fifteen, twenty, or thirty days later dose them again. If you don't re-dose them at the right interval, then all you are doing is making medicine-resistant parasites as they get hit with it, then rebound with immunity. (Kind of like people do with antibiotics, neh?)
Good luck, and as always, if he starts to act woogier than usual, please take him to a low-cost vet...one of the things my husband and I have learned is that it is far better to eat ramen for a few days and have a healthy cat than to eat well while one of the cats is suffering.
I'd take him to a vet for a regular series of shots. Unless the pet store provided paperwork, there's a good chance they only did those required by law, or simply lied about it. Pet stores selling animals without proper paperwork proving health/vaccination is a big problem nowadays. Laws have been changed recently to protect the purchaser.
Of course, they may not be lying and he could have picked up a parasite. But if two separate animals in different households from the same store have the same problem, it's probably a parasite they didn't get shots for.