Ambergris is a solid waxy substance originating in the intestine of the sperm whale (Physeter catodon). In Eastern cultures ambergris is used for medicines and potions and as a spice; in the West it was used to stabilize the scent of fine perfumes. It is illegal to use ambergris in the U.S. because the sperm whale is protected; however, it is used often in foreign markets. The substance is also contraband in India. It sells for up to $40,000 a kilogram.
Asafoetida is a plant. It has a bad smell and tastes bitter. That probably explains why it is sometimes called “devil's dung.” People use asafoetida resin, a gum-like material, as medicine. Asafoetida is also used in savory dishes, often to add a more full flavor by mimicking the taste of onions, garlic, egg, and even meat. It's a staple ingredient in Indian cooking, commonly used along with turmeric in lentil dishes like dal, and a variety of vegetable dishes.
Salt is both a seasoning and condiment but, salt is not a spice or herb since both of which are obtained from plants. Salt is a worldwide popular seasoning, yet it is not a spice. Instead, it is an organic mineral. Spices like black pepper are organic plant-based flavorings different from salt. Salt is a mineral compound that is organically found in nature. It is obtained by evaporation processes of saltwater or mined from salt rocks. Salt is still used as money among the nomads of Ethiopia's Danakil Plains. Greek slave traders often bartered salt for slaves, giving rise to the expression that someone was "not worth his salt." Roman legionnaires were paid in salt—salarium, the Latin origin of the word "salary."