The fur undercoat is removed using the Furminator to help with shedding and mats. The Furminator is a popular tool, but I'm not a fan of it because it may easily irritate skin if used incorrectly or too often. Additionally, I've discovered that it cuts through both the topcoat and the undercoat, leaving the topcoat too thin. A slicker brush or undercoat rake is what I use instead.