Tapioca is a plant product made from the roots of the cassava plant~also called manioc. It's a major product in Thailand and I saw "tapioca trees" all over the place. The plant itself isn't a tree, but they take the rootstocks and tie them into bundles which they set upright in the fields so they don't rot during the rainy season. Leaves sprout from the top of the bundle and the whole thing looks like a tree. The root has a poisonous acid in it that has to be removed by cooking. Those little balls are actually made++like risotto or "rice pasta". It's usually used to make sweet puddings here, but in the Orient it's used to make thick, savory soups. Like this one! Heat the stock to simmering in a large pan. Pour 1/2 cup of the hot stock into a bowl and stir in the pork. Return mixture to the pan. Add the garlic and fish sauce to taste, then add the tapioca and cook for 5 to 10 minutes. When the tapioca is clear, add the crab meat and season to taste with pepper. Remove from the heat. Line individual soup bowls with the lettuce. Pour in the soup and sprinkle with coriander leaves. From "Discover Thai Cooking" by Chaslin, Canungmai and Tettoni, Times Editions, Singapore. 1987. This is a simple, excellent soup and subject to all sorts of variations.