Eating grass often occurs when the cat needs to clean out its stomach by vomiting (maybe to get rid of furballs!). If your cat does not have access to grass, house plants or anything similiar will be used by your cat. Vomiting will occur soon after the cat has eaten grass. It has been said that cats eat grass to obtain "Folic Acid", something that cats need in minute quantities for its well-being. "Folic Acid" cannot be obtained from meat.