Mustard seeds are small, matt, hard, spherical, and either brown, white or black. When heated, they taste bitter, nutty, hot and aromatic. They are a key ingredient in some vegetable dishes and in pickles. In Bengal, they are often ground to make sauces for fish. Cooks in southern India fry a small quantity with other seasonings, such as cumin and curry leaves, before eating them – take care when you do this: the seeds pop in the hot oil and fly about with a life of their own. The spiciness of mustard seeds, no matter how pungent, does not linger, and they impart a rich, earthy taste to any dish.