Whilst grooming themselves, cats ingest dead hair that can get caught in their stomach. The enzymes in the stomach cannot break down this hair and it can create a blockage of the stomach and intestine. For this reason cats typically vomit to try and expel the hairball.  Feline flavoured laxative such as Aristopet Laxative or Laxapet are readily accepted by mouth by many cats and used two to three times a week will help to expel any hairballs.