Το Katsuobushi, which in Japanese means 'coal fish', is dried and smoked tuna fermented. The Katsuobushi is based in many soups and sauces in Japan. Today, usually circulates in pouches as small pink-brown chips. The katsuobushi holds the Guinness record for the hardest food world.

In this video, the user kiwami japan trying to make a sharp knife katsuobushi.