Cooking or cookery is the art or practice of preparing food for consumption with the use of heat. Cooking techniques and ingredients vary widely across the world, reflecting unique environmental, economic, and cultural traditions. Cooks themselves also vary widely in skill and training. Cooking can also occur through chemical reactions without the presence of heat, most notably as in Ceviche, a traditional South American dish where fish is cooked with the acids in lemon or lime juice. Sushi also uses a similar chemical reaction between fish and the acidic content of rice glazed with vinegar.