Some cat owners make the mistake of preventing their cat from eating grass. There are various reasons for this, one being that they think it makes their cat ill or upsets their stomach. This is an incorrect assumption and in fact the eating of grass followed by regurgitation is a perfectly natural behavior for all cats. Cats do not possess the ability to separate meat from fur bones or feathers before eating like we do so they have to eat the digestible parts along with the indigestible parts. When the cat has finished digesting what he can the rest has to be removed from the system. To try and pass this through the digestive tract could cause obstruction and severe illness so this is where grass eating comes in.