Cats naturally love to groom themselves. The tongue of a cat is covered with hook like prongs which capture loose hair as the cats grooms his coat. The hair is then swallowed and most of it passes through the digestive tract without a problem. However, if the hair gets left in the stomach, it can form a ball which the cat tends to vomit as a natural way to expel the hairball. Cats that are long haired or excessively groom are most likely to suffer with furballs. Sometimes cats who suffer badly with hairballs may need veterinary treatment as they can in become stuck and cause retching, intestinal blockages or constipation. If you have any concerns, please talk to your vet.