Whether you have an indoor or outdoor cat, one thing is for certain: your feline friend has probably nibbled on grass on more than one occasion. While it might seem like strange behavior -- especially when your cat throws up afterwards -- there's really nothing to worry about. Not only is there no evidence to suggest that grass will harm your cat, but many experts theorize munching on those long green blades can be beneficial for your cat.

http://www.petmd.com/cat/wellness/evr_ct_eating_grass